JP2011202959A - Dynamic viscoelasticity measuring instrument and dynamic viscoelasticity measuring method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an instrument and method capable of simply and inexpensively measuring viscoelasticity.SOLUTION: This dynamic viscoelasticity measuring instrument is equipped with a vibration part 13 for driving a contact element in a predetermined amplitude length and amplitude frequency so as to advance and retreat the same, a servo amplifier 22 for controlling the amplitude condition of the vibration part, an encoder 14 for measuring the amplitude state of the vibration part, an input control part PC for controlling the input signal to the servo amplifier in order to correct the deviation at the time when the output value outputted from the encoder is compared with a target amplitude condition and an operation part PC for operating the magnitude of load on the basis of the value inputted to the servo amplifier by the input control part. In the dynamic viscoelasticity measuring method, the actual amplitude state at the time of vibration of the vibration part is measured and the input value of the vibration part is compared with the input value in a non-load state to operate the increase quantity of the input value as load.

Description

  The present invention relates to an apparatus and method for measuring dynamic viscoelasticity.

  In recent years, in the food industry and the like, a device that evaluates mechanical properties for quality control is desired, and development of a device that is highly reliable and can be easily evaluated is eagerly desired. However, many liquids and solids have not a simple structure but a composite composition or structure, and exhibit viscoelasticity with viscosity and elasticity. Therefore, the evaluation of mechanical properties is not easy, and dynamic viscoelasticity measurement has been used as a method for evaluating viscoelasticity. This measuring method has been used exclusively for evaluating material properties in the industrial field such as plastics and paints (see Patent Document 1).

  However, since the apparatus currently used requires highly accurate measurement of strain and stress, the apparatus becomes very expensive, so that the application is limited to the research purpose. In addition, there are devices that target liquids and plastics and other hard objects, but there are few devices that target soft objects such as food. And as this kind of device, there were one using a giant magnetostrictive element (refer to Patent Document 2) and one using a piezoelectric element (refer to Patent Document 3), but this is also expensive. In addition, there is a problem in that the amplitude of the excitation unit is small and only a fine displacement can be obtained.

JP 2009-53107 A JP 2005-134295 A JP 2008-29111 A

  The above prior art uses a giant magnetostrictive element and a piezoelectric element, so that it is possible to measure viscoelasticity with high accuracy, but it does not require advanced precision as an evaluation of mechanical properties. In some cases, a measuring device that can be evaluated simply and inexpensively was desired. In particular, in the food industry, for example, it is only necessary to be able to evaluate that the viscosity is higher than a predetermined viscosity.

  The present invention has been made in view of the above-mentioned points, and an object of the present invention is to provide an apparatus and a method capable of measuring viscoelasticity easily and inexpensively.

  Therefore, the invention according to the dynamic viscoelasticity measuring device includes a vibration unit that drives the contact to move back and forth with a predetermined amplitude length and amplitude frequency, a servo amplifier that controls the amplitude condition of the vibration unit, and the vibration unit. Controls the input signal to the servo amplifier to correct the deviation when comparing the output value output from the displacement detector or encoder with the target amplitude condition. The gist of the present invention is a dynamic viscoelasticity measuring device comprising: an input control unit that performs a calculation of a load based on a value input to the servo amplifier by the input control unit.

  According to the measuring apparatus having the above configuration, the excitation unit is driven under the target amplitude condition, and even when the contactor contacts the measurement object and generates a disturbance, it can be driven under the target amplitude condition. it can. And the characteristic of dynamic viscoelasticity can be quantified by calculating the input load under the situation where the disturbance occurs.

  In the above invention, the input control unit may be an input control unit that executes an iterative control in which an output value for each predetermined period of amplitude of the excitation unit is compared with a target value and a correction value is sequentially fed back. .

  If it is the above structures, the amplitude condition of the excitation unit can be brought close to the target value early by feedback of the correction value, and the number of cycles to be sampled can be increased or decreased. The input control signal can be leveled. In other words, when the correction value is fed back for the output value for each cycle, if the output value is disturbed for some reason, it will be reflected in the input. Can be leveled.

  In addition, the calculation unit in each of the above inventions measures the current value supplied to the excitation unit, and calculates the change in thrust due to the load from the current value that is changed by comparing the current value with the current value in the no-load state. It can be set as the calculating part.

  With the above configuration, for example, the frictional resistance of each part is generated even in a no-load state, and therefore, only a load corresponding to a pure disturbance excluding this type of load should be measured. Can do.

  A voice coil motor can be used as the excitation unit. With such a configuration, the contact can be driven by the vibration of the target frequency, and the load on the contact can be converted as a current value.

  On the other hand, the present invention according to the dynamic viscoelasticity measuring method vibrates the vibration part that drives the contact to move back and forth with a predetermined amplitude length and amplitude frequency, and measures the actual amplitude state when the vibration part vibrates. The actual amplitude state of the excitation unit is brought close to the target amplitude condition, the input value of the excitation unit is compared with the input value in the no-load state, and the increase of the input value is calculated as a load. The gist is a method for measuring dynamic viscoelasticity characterized by the following.

  According to the measurement method having the above configuration, even when the contact is in contact with the measurement object, the load necessary for realizing the vibration of the contact by vibrating the contact with the target amplitude condition. Can be measured. The characteristic of viscoelasticity can be quantified by the load measured at this time.

  The step of approaching the target amplitude condition in the above invention may be a step by repetitive control in which the output value for each predetermined period in which the vibration exciter is amplified is compared with the target value and the correction value is fed back sequentially. it can.

  According to the above configuration, the output value output to the excitation unit is corrected as appropriate, and the excitation unit is driven in a state of approaching the target amplitude condition as the repetitive control proceeds. be able to. As a result, it is possible to make the amplitude state when there is no load coincide with the amplitude and phase when there is a load. And the difference of the thrust required for the drive of the vibration set when there is no load and the thrust required for the drive of the vibration set when there is a load can be calculated, and the viscoelasticity of the measurement object can be measured.

  According to the dynamic viscoelasticity measuring apparatus of the present invention, by measuring the magnitude of the load when the measurement object is brought into contact with the contact, it can be converted into a numerical value by converting it. . Therefore, the characteristics of dynamic viscoelasticity can be easily measured. The measuring device can be manufactured at low cost because the driving device can be realized by a small voice coil motor (hereinafter sometimes referred to as VCM) or the like.

  Further, according to the dynamic viscoelasticity measuring method of the present invention, by controlling the amplitude state of the vibration unit to the target amplitude state, the load on the vibration unit when a disturbance based on the measurement object occurs is obtained. Viscoelasticity can be measured, and can be realized simply and inexpensively.

It is explanatory drawing of the vibration apparatus which comprises embodiment of this invention concerning a dynamic viscoelasticity measuring apparatus. It is explanatory drawing of the control apparatus which comprises embodiment of this invention concerning a dynamic viscoelasticity measuring apparatus. It is a block diagram which shows the structure of a repetition control system. It is a block diagram which shows the structure of the repetitive control system when a disturbance acts. It is a block diagram which shows the structure of the repetition control system which uses a low-pass filter. It is a graph which shows the result of having measured the dynamic viscoelastic property of the gel chip. It is a graph which shows the relationship between the displacement when a gel chip is compressively deformed, and the detected thrust.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. An embodiment of the present invention relating to a dynamic viscoelasticity measuring device is roughly composed of a vibration device and a control device.

  As shown in FIG. 1, the vibration device includes a frame 11 installed on the base 1, a vibration base 12 projecting from the frame 11, and a vibration installed on the vibration base 12. The unit 13 is configured. The vibration unit 13 is configured by a driving device that swings at a predetermined frequency, and a VCM is used as an example. Hereinafter, an example in which a VCM is used to drive the excitation unit 13 will be described. The VCM excitation unit 13 has a VCM yoke (hereinafter may be referred to as a stator) fixed to the excitation base 12 and a coil (hereinafter may be referred to as a mover) is moved back and forth (vibration). Thus, the vibration of the mover is transmitted to the contact 16 at the lower end via the advance / retreat member 15 penetrating the stator. The advance / retreat member is slidably supported in the advance / retreat direction by a ball spline bearing 17 attached to the vibration base 12.

  A linear encoder 14 is provided on the coil side of the vibration exciter 13 so that the advance / retreat (vibration) state of the coil can be detected every predetermined time. The displacement detected by the linear encoder 14 is output to a control device described later.

  With such a configuration, when a current is supplied to the VCM, the coil vibrates, and the contact vibrates with the vibration. The current supplied to the VCM is such that the direction of the current changes in the forward and reverse directions according to a predetermined frequency.

  As shown in FIG. 2, the control device includes a personal computer (hereinafter abbreviated as “PC”) as the input control unit 21 and a servo driver 22 incorporating a servo amplifier. An interface (for example, a counter board) 23 for receiving a signal detected by the encoder 14 is connected (or built in) to the PC, and an interface for inputting / outputting an analog voltage (for example, an analog input / output (AIO)). ) Board) 24 is connected (or built-in).

  The servo driver 22 controls the VCM based on the analog voltage output from the PC. As an example, there is Pulse Width Modulation (hereinafter, PWM) control, and the case where PWM control is used will be described below as an example. Specifically, by modulating the pulse width, the on / off cycle is controlled and the current direction is controlled to be reversed in the forward and reverse directions. As a result, the VCM coil can be controlled so as to be able to advance and retreat, and can be vibrated at a frequency of about 5 to 15 Hz with an amplitude length of about 4 mm. At the same time, the detection value of the encoder 14 attached to the VCM can be received as a pulse signal and input to the PC. The detected pulse signal is digitized by an interface (counter board) 23 connected to the PC, and is used for control in the PC as output data.

  The input control unit (PC) 21 calculates an input value with reference to output value data for a preset target value. Specifically, with respect to the target value (a constant value), it is stored as output data from detection values for a predetermined period (for example, three periods), this output data is compared with the target value, and the deviation is corrected. As a value, the initial input value is corrected and the value is output to the servo driver. Note that the PC 21 includes a calculation unit, and can calculate a thrust from an output value described later.

  The input control unit 21 uses the repetitive control shown in FIG. As shown in this figure, the repetitive control is a control method in which the output value is fed back as a deviation of the target value, the initial or previous input value is corrected and used as the next input value. An output value obtained by detecting the actual driving state of the VCM driven by the immediately preceding input value detects an amount of deviation from the target value, and this is corrected as a correction value for the immediately preceding input value. Repeating the next input value is repeated. Since this is a control method for approaching the target value while repeating the correction of the input value, this is called repetitive control.

  Here, conditions for converging the deviation to zero in the control system as shown in FIG. 3 will be described. First, the relationship between each element can be expressed by the following equations (3.1) to (3.3).

When the above formulas (3.1) to (3.3) are arranged, the following formula is obtained.

From the above equation, the deviation converges to zero under the condition that the following equation (3.1) is satisfied at all angular frequencies ω included in the input of the control system.

Next, FIG. 4 shows the configuration of the control system when there is periodic disturbance (resistance due to the measurement object). As shown in this figure, when the disturbance D (s) is continuously applied to the control system, the output Z (s) due to the disturbance D (s) is eventually included in the output Y _n (s). Therefore, even in this case, if the condition of the above equation (3.1) is satisfied, the deviation is converged to zero.

Moreover, it can be set as the structure which adds a low-pass filter process to the said control system. This corresponds to a case where high-order frequency components are generated for some reason by repeating the repeated control a plurality of times. Since such high-frequency components can be generated by disturbances such as the gain of the servo driver, low-pass is performed on either the output or the deviation (correction value) in order to perform output that eliminates high-frequency components not included in the input signal. Filter processing is performed. An example of the configuration of such a control system is shown in FIG. The control system shown in this figure performs the low-pass filter process for the deviation E _n (s), but can also process the output Y _n (s).

  As described above, since the deviation due to the disturbance can be converged even in the presence of a periodic disturbance, the load on the VCM (measurement target is measured by measuring the change in the current value in the repetitive control leading to the convergence. The viscoelasticity of the object can be calculated. That is, since the thrust of the VCM is proportional to the current, the load can be easily calculated based on the current value changed (increased) from the current value in the no-load state.

  Next, the relationship between the phase difference and the detected value will be described. As described above, the thrust of the VCM can be calculated by a change in current, and the vibration state of the mover of the VCM is measured by the encoder 14, so that the application of thrust to the VCM and the actual vibration state change with time. Can be detected. In the no-load state, there is no change in current, so the thrust does not change. However, when a load acts on this, in order to change the mover of the VCM to the target state, the thrust is changed by changing the current. Give. In other words, the contactor is lowered by lowering the mover of the VCM, and the contactor compresses the object. At this time, the thrust required for compression is achieved by the change in the current value described above, but the movement of the actual contact (ie, the VCM mover) depends on the timing of thrust application according to the viscoelastic characteristics of the object. May be different between.

  Specifically, when the object is an elastic body (particularly a pure elastic body), the elastic body is deformed as the thrust is increased, and the elastic body is restored by reducing the thrust. The mover vibrates at the same timing as the thrust application. On the other hand, in the case of a viscous body, the viscosity acts immediately after the thrust is applied, and the vibration of the mover is delayed. This is the same when the thrust is increased or decreased. Therefore, a phase difference is generated between the change in thrust with the passage of time at this time and the actual vibration of the mover with the passage of time. This is due to the damper characteristic that is a characteristic of the viscous body. When the phase difference is 90 °, it is a purely viscous body, and when it is a viscoelastic body, it falls within 0-90 °.

  Next, viscoelastic characteristics will be described. Evaluation of viscoelasticity is normally performed by storage elastic modulus, loss elastic modulus, and loss tangent. Therefore, these relational expressions are shown below.

  When the viscoelastic property of the viscoelastic body is measured using the above equation, the stress (σ) is measured by thrust, and the phase angle (δ) can be calculated by the phase difference between the input value and the output value. The strain (ε) can be calculated from the amplitude of vibration by the excitation unit. That is, it can be calculated from the thickness (L) and amplitude (b) of the object with respect to the direction of vibration by the excitation unit (the direction in which the contact is advanced and retracted). The strain (ε) is calculated by the following equation. Then, viscoelastic characteristics can be obtained by calculating these numerical values.

  As described above, according to the dynamic viscoelasticity measuring apparatus of the present embodiment, the contact is vibrated with the amplitude length and the amplitude width PWM-controlled by the output signal, and the vibration state of the vibration exciter 13 at that time is determined by the encoder 14. The input control unit 21 repeatedly controls the corrected next input value so that the excitation unit 13 after repeating a plurality of times can be compared with the target amplitude condition. It will approach the amplitude condition. Then, the thrust (stress) generated by the excitation unit 13 is calculated by calculating a change in current when the thrust is applied to the excitation unit 13 using an operation unit (not shown, but provided in the PC). Is done. Then, the strain can be calculated from the amplitude length of the excitation unit 13, and the phase difference (phase angle between stress and strain) can be calculated from the input value to the excitation unit 13 and the measurement value by the encoder 14. It becomes possible to measure each characteristic of dynamic viscosity, dynamic elasticity, and dynamic viscoelasticity. Such a processing method represents an embodiment of the dynamic viscoelasticity measuring method of the present invention.

  Since the thrust of the excitation unit 13 is calculated from a change in current, there may be a slight amount of noise depending on the load amount for moving the coil of the VCM, the friction coefficient of each unit, and the like. Therefore, a more accurate measurement value can be obtained by using the difference when the previously measured elastic body or viscous body is measured as a correction value and correcting the difference in the calculation unit 21. In addition, when noise is included in the current value flowing through the excitation unit 13, the phase difference can be calculated by performing noise cut by developing the first-order Fourier series of the current value.

  Furthermore, a change in current for applying thrust to the excitation unit 13 may be referred to as a compensation current value, and this compensation current value increases when a load (disturbance) is received from a no-load state. Current value. Thus, the difference in the current value in the state increased from the no-load state is the compensation current, and in the present embodiment, the thrust is calculated based on the value of the compensation current. A means for calculating a thrust by an analog voltage value) may be employed.

  Although not specifically described, an interface with an external display device is connected to the control device (see FIG. 2), and a monitor or a printer is connected to the control device to display it on the monitor or the calculation result is a numerical value. Can be printed. Moreover, although the frequency by the vibration part 13 is variable, it will adjust to the frequency suitable for a measurement. When operated at a frequency between 3 and 20 Hz, a considerable measurement result can be obtained. However, when dynamic elastic measurement is performed on an elastic body and when dynamic viscosity measurement is performed on a Newtonian fluid, the frequency is obtained. Therefore, any frequency can be arbitrarily selected and measured. On the other hand, when dynamic viscoelasticity measurement is performed on a viscoelastic body, since it depends on the frequency, viscoelasticity at different frequencies can be evaluated for each substance.

[Experimental example]
Next, an experimental example for measuring dynamic viscoelastic properties of a specific viscoelastic body will be described. The various devices used in this experiment are as follows.
<Excitation unit (VMC)>
X-1741 made by NEOMAX (stroke 4mm, rated thrust 6N)
<Linear encoder>
Mercury 2000 (resolution: 0.833 μm) manufactured by Micro E Systems
<Servo driver>
Servo driver Movo SVFM-DSP (servo cycle 16kHz)
<Counter board>
CONTEC CNT32-8M (PCI) (resolution 32 bits)
<Analog input / output (AIO) board>
CONTEC AIO-163202F-PE (16-bit resolution)
The object used for the experiment was silicon gel (GC-8 manufactured by Taika Co., Ltd.), and the gel chip was a rectangular parallelepiped having a length and width of 14 mm and a height of 10 mm. A contact having a circular shape with a tip shape of 20 mm in diameter was used.

  As the target values in the experiment, the amplitude was set to 0.2 mm, and eight types of frequencies were arbitrarily selected from 3 to 20 Hz, and the respective frequencies were operated. The result is shown in FIG. From this experimental result, it became clear that the dynamic viscoelastic characteristic according to the frequency was measured. FIG. 6 shows the relationship between the displacement and the detected thrust when the gel chip is compressed and deformed. As is clear from this figure, there is a phase difference in the relationship between thrust and displacement. Accordingly, it has been found that the viscosity can be measured. From the above, it is possible to measure viscoelasticity in the above apparatus.

1 Base 11 Frame 12 Excitation Base 13 Excitation Unit (VCM)
14 Linear Encoder 15 Advance / Retreat Member 16 Contact 17 Ball Spline Bearing 21 Control Unit (PC)
22 Servo Driver 23 Counter Board 24 Analog Input / Output (AIO) Board

Claims (6)

An excitation unit that drives the contact to move back and forth with a predetermined amplitude length and amplitude frequency, a servo amplifier that controls the amplitude condition of the excitation unit, an encoder that measures the amplitude state of the excitation unit, and an output from the encoder An input control unit that controls an input signal to the servo amplifier in order to correct a deviation when the output value is compared with a target amplitude condition, and a value input to the servo amplifier by the input control unit. A dynamic viscoelasticity measuring apparatus comprising: a calculation unit that calculates a size. The input control unit is an input control unit that performs an iterative control in which an output value for each predetermined period with the amplitude of the excitation unit is compared with a target value and a correction value is sequentially fed back. The dynamic viscoelasticity measuring apparatus according to claim 1. The calculation unit is a calculation unit that measures a current value supplied to the excitation unit and calculates a change in thrust due to a load from a current value that is changed by comparing the current value with a current value in a no-load state. The dynamic viscoelasticity measuring apparatus according to claim 1, wherein the apparatus is a dynamic viscoelasticity measuring apparatus. 4. The dynamic viscoelasticity measuring apparatus according to claim 1, wherein the vibration unit is a voice coil motor. A vibration unit that drives the contact to move forward and backward with a predetermined amplitude length and amplitude frequency is vibrated, the actual amplitude state when the vibration unit vibrates is measured, and the actual amplitude state of the vibration unit is determined as a target. A dynamic viscoelasticity measuring method characterized by causing an amplitude condition to approach, comparing an input value of the excitation unit with an input value in an unloaded state, and calculating an increase in the input value as a load. The step of approaching the target amplitude condition is a step by repetitive control in which an output value for each predetermined period in which the excitation unit swings is compared with a target value, and a correction value is sequentially fed back. The dynamic viscoelasticity measuring method according to claim 5.

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