CH691196A9 - Process for viscoelastic characteristics of measuring substance or mixed and apparatus for measuring the implementation process. - Google Patents

Description

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Description

The present invention relates to a method for measuring the viscoelastic characteristics of substances or mixtures and to measuring equipment for carrying out the method.

The need to know the viscoelastic properties of substances or mixtures is expressed in various and numerous fields such as for example the chemical, pharmaceutical, cosmetic, food, petrochemical and metallurgical industries. This need is obviously not new, many proposals have been made for measurement methods and their implementation devices.

Without claiming to exhaust the subject, we can notably mention the techniques aimed at measuring the flow properties of the tested sample. These techniques apply to Newtonian substances or mixtures such as milk for example.

When it is a question of measuring the viscoelasticity characteristics of non-Newtonian substances or mixtures, that is to say of pastes and other ointments, the measurement of the flow cannot be applied because the flow of such samples is zero or not reasonably measurable . The same applies to thixotropic mixtures, the typical example of which is the yogurt.

Without being able to usefully measure a flow, we tried to highlight the shear parameters of the material tested. The most recent devices, often called rheometers, use rotor-stator systems. The sample is placed in a stator in the form of a bucket or cylinder in which a rotor is engaged which may have various shapes depending on the nature of the experiment, but which generally appears as a cylinder terminated by a cone. The rotor is set in motion by a motor and we read on a scale the value of a resistance caused by the viscosity of the material located in the air gap between rotor and stator. Basically, the less the rotor is braked, the lower the viscosity.

This type of process and apparatus are satisfactory when it comes to assessing the viscosity of different mixtures comparatively. Thus, if several samples of the same cream are produced, for example by varying the proportions of one of the ingredients, these systems make it possible to qualify and order the samples from the least viscous to the most viscous, and therefore to choose the dosage which agrees.

On the other hand, these systems do not allow a valid comparison over time of the consistency properties of a single mixture, tested at various degrees of aging or maturity.

The main handicap, in fact prohibitive, of rotor-stator systems for measuring the evolution of viscosity in the tenps is that they require manipulation of the mixture and its introduction into the stator. This manipulation has an influence on the consistency of the sample. In other words, the use of such systems implies that the parameters which one is precisely seeking to determine with the greatest possible precision are modified before measuring them. Of course, one could consider filling, during manufacture, several rotor / stator systems with the mixture to be tested. It should also be guaranteed that the rotor / stator binomial remains fixed during positioning on the rheometer to avoid causing an alteration of the three-dimensional (non-Newtonian) structure of the mass to be measured. However, this procedure is not practical. Nor does it offer sufficient guarantees, since the simple manipulation of the pre-filled rotors / stators influences the results. Thus, the measurements cannot, by definition, reflect the state of the sample in its actual packaging, as actually placed on the market.

These observations have led to an attempt to express the viscosity or rather the consistency by measuring the penetration parameters in a sample of a calibrated probe, the penetration surface of which is both flat and of determined dimensions. This path, called penetrometry or consistometry, has also given rise to the development of measurement methods and devices intended to implement these methods.

For the most part, the known apparatus adapted to consistometry or penetrometer work on the same principle. It involves inserting a probe of a determined size and weight, for example an inverted cone weighted with a determined quantity of shot, into the mass of the sample and expressing its consistency according to various systems of measurement, in general not compatible. These systems can be based for example on the time taken by the probe to complete a certain route, on the force to be exerted for the probe to complete a certain route in a certain time, at a determined temperature.

As regards more particularly the methods or devices based on the measurement of a force to be exerted, the measurement of the resistance offered by the mixture to the penetration of the probe is perceived by the apparatus, more precisely by one or more dynamometers installed in the device and this data or measurement is translated into analog or digital form to allow reading. These are the systems deemed to be the most advanced and the most efficient.

However, these systems offer significant drawbacks. Firstly, using dynamometers, these systems are directly dependent on the qualities and limits of these instruments. To overcome a direct dependence between the quality of the measurement and the quality of the instrument, we sought to combine several dynamometers so as to avoid that the results are too directly dependent on a single instrument. Thus, systems have been proposed, the best at present, in which several dynamometers are combined, the penetration measurement not being provided by a reading on the dynamometers themselves, but by a metric scale making it possible to measure the result of the displacement of a set of several dynamometers. If this system has the merit of making the measurement of the random factor of an isolated dynamometer less dependent, it has

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Dant you disadvantage to disguise somewhat the nature of the measure because it becomes dependent not only on the quality and stability of the dynamometers, but also those of their assembly, which is not without effect.

In addition, it is particularly difficult to detect a possible anomaly in a dynamometer in a network, which only adds to the difficulty that there is in diagnosing a possible imbalance of a dynamometer, then in remedying it. In short, if the system is perfect, its measurements are perfect; unfortunately, it is extremely difficult to verify both the hypothesis and its consequence. Finally, it will also be noted that, if this system can be reliable for an isolated device, it is less, if not more at all, if it is a question of comparing measurements of the same kind, performed by two identical devices which have despite everything, each has their own particularities. In other words, two a priori identical devices will only very rarely provide identical measurements if one is located in a different place, country or continent from the other, this because of the impact of the climate on performance. dynamometers.

The object of the present invention is to propose a method for measuring the consistency based on consistometry or penetrometry, as well as an apparatus for implementing the method, both being intended to eliminate an element of constant uncertainty so far, using as a benchmark a standard justly known for its invariability and the ease of calibrating instruments, both in time and in space.

The characteristics of the process according to the invention are set out in claim 1; those of an embodiment in claim 2. The characteristics of the apparatus according to the invention are described in claim 3; those of embodiments more particularly in claims 4 to 18.

A description is given below of the process and an example of apparatus according to the invention, based on the drawing in which:

fig. 1 schematically represents a simplified version of the apparatus according to the invention;

fig. 2 shows in schematic view, a detail of the motor unit of the apparatus according to the invention;

fig. 3 shows a version of the apparatus according to the invention supplemented by an analog block and a graphic recorder;

fig. 4 is a block diagram of the apparatus in its version illustrated in FIG. 3;

fig. 5 shows the apparatus according to the invention as produced in a compact device which can be connected to a computer;

fig. 6 illustrates a graphic recording of a measurement sequence as practiced on a first product by means of the apparatus illustrated in FIG. 3;

fig. 7 illustrates a graphic recording of a measurement sequence as performed on a second product by means of the apparatus illustrated in FIG. 3; and fig. 8 illustrates a curve of measurements carried out on the same product (emulsion system, O / W cream) at various degrees of aging.

The consistency measurement process is of course intimately linked to the means used to apply it. The description which follows gives, in detail, the particularities of said means and each will understand as the description progresses how these means participate in the process.

However, before starting the description proper, we briefly outline below, in broad outline, the essential features of the method according to the invention.

The process involves placing a sample on a scale, then placing a calibrated probe in contact with the sample substance and taring the scale to zero. The probe is then lowered into the mass of the sample according to a predetermined stroke and speed.

The measurement of consistency is expressed by the indication of the measurement of resistance expressed in a unit, as given by the balance.

The balance is a very old instrument, which has been the subject of numerous improvements and which is today one of the most reliable instruments that exist. In addition, it is very easy to determine whether a balance gives an exact measurement. It is also very easy to perfectly adjust an unbalanced balance, in particular an electronic balance. Finally, the scale is an instrument available everywhere and therefore very widely used.

Thus, by using a balance to express the measurement of consistency, one directly benefits from all the advantages linked to this instrument with regard to precision, consistency, calibration and reliability.

In fig. 1, there is a base 1 which will give its seat to the entire measurement system.

There is also a support column 2 on which an adjustment and fixing ring 3 can slide, which can be locked at the desired height on the column. This fixing ring serves as a support for a motor box 4, the content of which will be described later, but which it can already be noted that it comprises a stepping motor with threaded pins. This motor will bring down a push rod 5 on which is fixed a probe 6 which will penetrate into the substance whose consistency must be measured. It can already be noted that the stroke of the spindle 5, and therefore the movement imparted to it by the motor, are subject to five preselections with regard to the stroke. The indications which follow are given by way of example and can obviously be modified as required. Five predetermined strokes are chosen at 10, 20, 30, 40 and 50 mm.

On the other hand, the lowering speed of the spindle is also the subject of predetermined values. We have retained the values of 0.05 - 0.1 - 0.25 - 0.5 and 2.5 millimeters per second, which are given here by way of example.

We finally recognize in fig. 1 the container 7 of the test substance, as well as the balance 8,

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which will allow the consistency to be read, as expressed when the probe 6 has reached the preselected descent depth, according to the speed also preselected. It is preferable to use an electronic balance with a timed value, such as the Mettler 4800 model for example.

In the rudimentary configuration of the apparatus, as shown in fig. 1, the measurement process can be carried out as follows. We start by placing the container with its contents 7 on the scale 8. We then choose a calibrated probe 6 which can have various shapes, including in particular that of a cylinder. The shape of the probe can end with a plate or flat face whose surface is determined and chosen. The probe is then fixed on the push rod 5 and, by means of the adjustment ring 3, the motor unit is lowered manually until the underside of the probe 6 is flush with or slightly penetrates the surface of the material to be measured contained in the container 7.

Then press the balance control bar to perform automatic taring and zeroing.

The length of the stroke is then selected from the predetermined values, then the speed of movement of the probe is also selected from the predetermined values.

We then start the engine which will lower the probe at the chosen speed until the chosen stroke is reached. At this precise moment, the balance indicates a certain value, which is used as an indication of the value of consistency. One could of course simply read the said value on the display of the balance, but it is preferable to fix this value on an electronic device which allows both your display and storage. This operation can advantageously be carried out by the computer in the event that such a connection is provided.

Provided that care is taken to reproduce exactly the temperature conditions of the experiment and that the same predetermined data are used with regard to the travel and the speed of the probe, various samples of a same product at sessions' of measurements practiced at various stages of aging of the product.

The temperature having an influence on the consistometric measurements, an electronic thermometry system can be associated with the probe. This system, which will be described in more detail in connection with FIGS. 3 and 4, allows the measurement of the temperature at the point of contact between the probe and the sample. The electronic measurement allows the conservation of the measured values and also allows their storage and their computer processing. It is thus possible to also translate the temperature measurement, in particular in graphical form, in combination or not with the representation of other measured quantities.

The constancy of the penetration speed and the travel of the probe will make it possible to obtain comparable values over time, all the more so since the precision and calibration of the balance are also its guarantors.

In fig. 2, there is a detail of the motor unit 4 and of the face which it presents to the user. A first push button 9 makes it possible to control the ascent of the push rod 5. The push button 9 is associated with a light diode 10 which will remain on until the motor spindle has reached its upper internal stop. A second push button 11 controls the descent of the push rod 5 and is associated with a light diode 12 which will remain lit throughout the descent movement of the push rod. A third push button 13 controls the stopping of the engine, both when going up and when going down.

We can also refer to fig. 4 consisting of the assembly block diagram as shown in FIG. 3 and which allows a better understanding of the explanations given below in relation to FIG. 2.

The up 9 and down 11 pushbuttons are combined with control relay circuits which store the down and up orders and authorize or not the routing of the pulses to an address counter. As indicated above, the box includes a motor capable of actuating the push rod and the probe in the power, speed and amplitude range corresponding to the present application. Motors of various types can be used. In fact, almost any motor can be used as long as pulse counting is possible, whether it takes place anyway (AC motor, stepper motor) or is the result of '' a specially dedicated pulse generator (DC motor). In the example described, a stepping motor 14 is used which comprises four windings supplied in a defined sequence through groups of power transistors mounted in Darlington. A motor, such as the Sonceboz 7220 R010 model, which has a maximum stroke of 63.5 mm, a maximum force of 15.3 N, a linear pitch of 0.0508 mm and which operates at 12 volts is perfectly suited for an application more particularly intended for testing creams, especially cosmetics. The switching sequence is determined by a program originating from an EPROM memory 27C16 and is delivered to the group of transistors and coils by the DATA bus of the memory. The memory receives its addressing instructions from a 0-15 counter of the 74LS93 type, itself receiving the pulses, allowing the change of state of the address inputs of the memory 27C16, of a pulse multiplier assembly. constituting the system clock. This clock is based on the initial oscillation of a 1 MHz quartz with its logic oscillator circuit 74C14, followed by six frequency divider stages fitted with 74LS90 circuits. By a speed switch 15, it is possible to connect the input of the addressing counter 74LS93 to various points of the last stages 74LS90 of the frequency divider and thus to take pulses whose cadence determines the speed of change of the addresses of the program of the mo5

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tor, therefore its internal speed of rotation and therefore the speed of descent or ascent of the push rod and the probe.

The reversal of the direction of operation is obtained by using bits 0 to 3 of memory 27C16 for lowering and bits 4 to 7 for raising. This selection is made by logic switching using a 74LS157 multiplexing.

The switching enabling the motor to be engaged, the direction of travel control and an automatic stop circuit are located between the speed selector 15 and the addressing counter 74LS93.

The selection of the depths to be reached, that is to say the travel of the probe, is carried out by means of a switch 16. This is connected to two 74LS93 counters whose binary outputs lead to the inputs of 74LS154 decoders allowing the counting-decoding of numbers between 0 and 255. This set is completed by two dividers by two and thus allows to count up to 1024 pulses maximum. The depth switch 16 is double. One half allows to take the logical states on the 74LS154 decoder of the units (0 to 15) and the other half allows to take the logical states on the second 74LS154 decoder dedicated to sixteen.

Each chosen depth thus corresponds to a logic state taken from each of the two 74LS174 decoders. After inversion, these states are brought to the input of a Nand 74LS00 circuit, one output of which activates a monostable circuit 74121, which itself actuates a motor stop relay. The stop push button 13 is double cut and allows the interruption of the supply of pulses to the addressing counter 74LS93 and the resetting of this counter. A lever switch 17 having two positions A and B allows, when it is in the first position A, the resetting of the counters 74LS93 for depth counting. When in position B, the switch allows depth counting.

The panel of the motor box also comprises a light diode 18, translating into light pulses the control pulses of the linear motor. A liquid crystal display counter 19 displays the count of the bytes or double bytes of pulses delivered to the motor. This display allows you to check the depth reached by changing a number. The numerical values which are written there are not metric data, but only the counting of the pulses. A lever switch 20 having two positions C and D allows the pulse counter to be zeroed in one of the positions, this in particular when the motor spindle is at its maximum height stop. In the other position, this lever authorizes counting.

In fig. 3, we find elements already encountered in FIG. 1, in particular the motor unit 4, the adjustment and fixing ring 3, as well as the balance 8. A digital-analog converter 21, for example a Mettler GA37 converter, is connected to the balance.

This digital-analog converter is also connected to an analog block 22 whose indicator translates into analog form the values, obviously identical, which are displayed both on the balance 8 and on the converter 21.

The analog block is also connected to a graphic recorder which allows the plotting of the curve of the values recorded by the balance throughout the descent of the probe into the material to be tested.

We also note the presence of a connection cable 24 between the motor box 4 and the analog unit 22.

Finally, fig. 3 also shows the temperature measurement system, which is composed of a thermistor 25, here incorporated into the probe, but which can also be independent of the probe. The thermistor is connected to an analog amplification circuit 26, itself connected to a display member 27 which can be digital or possibly analog. The device receives an order to store the temperature value when the predetermined travel of the probe is reached, ie at the end of the consistometric measurement.

It should be noted that the analog block is connected to a power supply not shown here.

The connection cable 24 makes it possible on the one hand to supply the motor unit 4 and on the other hand to send the signal to interrupt the supply of the motor at the precise moment when the pulse counter reaches the number which corresponds to the depth that has been selected.

It has been indicated that, at the start of the measurement, the lower surface of the probe is brought manually into contact with the surface of the substance to be tested. In practice, the motor box is lowered until the scale, which is previously tared, ceases to indicate the zero value. Once the contact is established, the balance is reset to zero. This operation is made automatic in the sense that the counting of the predetermined downward travel of the probe does not start until the timed value given by the balance becomes different from zero, by contact of the probe with the mixture to be measured. A comparator connected to the internal electronics of the balance allows on the one hand the sending of a signal to reset the pulse counter of the motor and a command to stop the motor temporarily and on the other hand initiation of the automatic taring procedure for the balance. The motor is then replenished and controlled as already described as soon as the balance has completed its internal taring procedure and displays the zero value again.

Fig. 4 consists of the block diagram of the assembly as shown in FIG. 3 and does not call for particular comments, except that the various elements and components indicated in the commentary of FIG. 2 are indicated.

The apparatus has so far been described as a combination of various dissociated elements. The apparatus according to the invention is in fact intended to constitute a single and integrated apparatus comprising all the elements described so far. Fig. 5 gives a representation of this integrated apparatus which can take advantage of several ways a

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link with a microcomputer. First, some of the functions assumed by components or instruments in the variant of FIG. 3 are entrusted to the computer. This involves, for example, using the computer's internal clock instead of installing one in the device. Similarly, the management of the parameters and of the commands and pulses delivered to the motor can be entrusted to software.

The connection of the measuring equipment to a microcomputer is ensured either by the use of an RS232 link or by the direct connection of free ports of the computer.

Besides the possibility of entrusting the computer and its specific software with certain of the necessary functions, the advantage of interconnection also stems from the possibility of using databases and programs such as spreadsheets to store the parameters of measurement of each product tested, such as in particular the depth of stroke, the speed of the motor and the size of the probe, but also the results of the measurements as supplied by the electronics of the balance and by the thermometer. It will be added that the presentation of graphs illustrating the values of the measurements and their comparison over time, such as those which are the subject of FIGS. 6 to 8, can be performed using the usual computer peripherals and no longer requires digital-analog conversion.

Fig. 6 is a graph of a measurement made on a sample of 1/4 fat Tilsit cheese. The average temperature is 13 ° C. The probe used has a diameter of 2 mm and the stroke depth is 20 mm. The probe's lowering speed is 0.1 mm / s.

Fig. 7 is a graph of a measurement carried out on a sample of cosmetic cream. The average temperature is 13 ° C. The probe used has a diameter of 15 mm and the stroke depth is 5 mm. The probe's lowering speed is 0.5 mm / s.

Fig. 8 is a curve reflecting the results of several measurements taken at different time intervals, but always under the same conditions, on a sample of cosmetic cream. The abscissa expresses the duration in days and the ordinate measures it in grams read on the balance at the end of the probe stroke. All the indicated measurements are carried out at a temperature of 20.5 ° C. The probe used has a planar contact face whose surface is 1 cm2, the preselected depth is 30 mm and the probe's descent speed is 0.25 mm / s.

The advantages of the measuring method and of the apparatus according to the invention are to offer a practical and reliable possibility of carrying out consistency measurements both comparative of various products at the same time, and comparative of the same product at various times. by offering the guarantee that the unit of measurement, at constant parameters, does not induce an undetectable error, this due to the use, to express this measurement, of a balance and the ability to always calibrate exactly this instrument. Thus, thanks to the present invention, it is possible to express the consistency of essentially non-Newto-Nian mixtures in a universal and universally verifiable unit, one kilo remaining one kilo, wherever the measurement is made.

Claims (18)

Claims 1. A method of measuring the viscoelasticity characteristics of substances or mixtures, characterized in that to determine these characteristics, a sample to be tested is placed on the pan of a balance and in that a sample is made to penetrate into this sample calibrated probe, according to a previously chosen stroke and speed, and in that the measurement of consistency is collected by reading the value indicated by the balance at a predetermined time during the stroke of the probe. 2. Measuring method according to claim 1, characterized in that one carries out the reading of the value indicated by the balance at the precise moment when the probe has traversed the entire predetermined stroke which it must accomplish in the mass of the sample. 3. Apparatus for implementing the method according to one of claims 1 and 2, characterized in that it comprises a first element consisting of an electronic balance and in that it comprises at least a second element consisting of '' a motor imparting a linear movement to a probe and in that it comprises an electronic motor control device comprising at least the members necessary to predetermine the stroke of the probe and the speed of its movement of penetration into a sample placed on the balance. 4. Apparatus according to claim 3, characterized in that the motor is a stepping motor. 5. Apparatus according to one of claims 3 and 4, characterized in that the control device comprises a member for counting pulses delivered to the motor by the control device. 6. Apparatus according to claim 5, characterized in that the stroke of the probe is determined by counting the number of pulses delivered to the motor by the control device. 7. Apparatus according to one of claims 3 to 6, characterized in that it comprises a clock delivering a frequency signal to the control device. 8. Apparatus according to claim 7, characterized in that it comprises a member for dividing the frequency signal delivered by the clock and thereby determine the frequency of the pulses delivered to the motor and the speed with which the motor prints its movement with the probe, respectively the speed of penetration of the probe into the sample. 9. Apparatus according to one of claims 3 to 8, characterized in that the balance is coupled to the electronic control device. 10. Apparatus according to claim 9, characterized in that the control device is shaped so as to issue twice a taring command to the scale. 5 10 15 20 25 30 35 40 45 50 55 60 65 6 11 CH 691 196 A9 11. Apparatus according to claim 10, characterized in that the control device comprises means arranged to provide the balance with a first taring command when the sample is placed on the balance, either before the probe is in contact with the sample, and a second taring command automatically triggered at the precise moment when the contact between the probe and the sample is revealed by the first non-zero value indicated by the balance after the first taring. 12. Apparatus according to claim 11, characterized in that the control device comprises means arranged to provide the pulse counting member, a zeroing command triggered automatically at the precise moment when the contact between the probe and the The sample is revealed by the first non-zero value indicated by the balance after the first taring, so that the counting of the pulses, which determines the stroke of the probe, begins exactly at this moment. 13. Apparatus according to one of claims 3 to 12 characterized in that it comprises a temperature measuring member. 14. Apparatus according to claim 13, characterized in that the temperature measuring member comprises a thermistor. 15. Apparatus according to claim 14, characterized in that the thermistor is placed on the probe. 16. Apparatus according to one of claims 3 to 15, characterized in that the apparatus is connected to a computer arranged to manage, by specific software, all or part of the motor and / or balance control functions. 17. Apparatus according to claim 16, characterized in that it comprises means of connection to a computer arranged to manage, by specific software, all or part of the control functions, including the counting of the pulses delivered to the motor, the delivery of a frequency signal and its division, the delivery to the balance of the first taring command when the sample is placed on the scale and the issuance of the second taring command triggered automatically at the precise moment when the contact enters the probe and the sample are revealed by the first non-zero value indicated by the balance after the first taring, as well as the simultaneous zeroing of the pulse counter and finally the collection of the value indicated by the balance at the precise moment when the pulse counter reaches a predetermined number. 18. Apparatus according to claim 17, characterized in that it is shaped to be connected to a computer which manages by specific software the collection of the temperature value indicated by the thermistor. 5 10 15 20 25 30 35 40 45 50 55 60 65 7