JP2000314695A - Durable transducer for measuring viscoelasticity - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress, for example, a damage due to handling or the like of an elevator to a minimum limit by providing a means for limiting a movement of a probe member except a desired direction along a probe shaft. SOLUTION: This viscoelastic transducer comprises an annular spring assembly 20 constituted, for example, of two annular springs made preferably of beryllium copper adhered to an inside ring and an outside ring by soldering or the like. An outer edge of the assembly 20 is adhered to a pole 14, and the inside ring constitutes a mechanical probe moving in the transducer together with a probe adapter hub 18, a coil 16 and a disposable probe 24. Thus, lateral rigidity is given to the mechanical probe. A magnet 12 limits an inward deviation. A cover 22 limits an outward deviation. Thus, the assembly 20 is prevented from being excessively deformed when the probe 24 is attached or detached.

Description

DETAILED DESCRIPTION OF THE INVENTION

FIELD OF THE INVENTION The present invention relates generally to an apparatus for making viscoelastic measurements, and more particularly to an improved vibrating viscoelastic transducer for measuring the viscoelastic properties of fluids and gels. .

BACKGROUND OF THE INVENTION Viscous viscosity and viscoelastic analyzers are well known in the art. These analyzers typically incorporate a mechanical probe member that is driven to operate in a vibrating state or periodically. The analyzer comprises several means for imparting movement to the probe member and means for monitoring the displacement or movement of the probe. Most used designs incorporate an electrical means for driving the mechanical probe and an electrical means for monitoring the operation of the probe. The mobile probe is immersed in the fluid or gel to be measured. The operating characteristics of this mobile probe are:
Affected by the viscosity and viscoelastic properties of the material under test.
Changes in the operating characteristics of the probe in response to the test sample are monitored and processed by an analyzer that determines the viscoelastic properties of the test sample. Components of the drive mechanism or circuit,
The mechanical probe and the motion detection mechanism together constitute a transducer. The transducer has a response characteristic relating the input drive signal to the output operation signal. The response of the transducer depends on its physical design and the viscoelastic properties of the material under test. Transducer characteristics can be expressed using mechanical or electrical operating characteristics. US Pat. No. 4,341,1 issued to Husar
No. 11 uses the relationship between frequency and mechanical displacement to characterize transducer operation. Such a characteristic is shown in FIG. From an electrical design perspective, it is often desirable to characterize the operation of the transducer in terms of electrical impedance. FIG. 5 shows the relationship between the frequency and the change in the electrical impedance in the case of the viscoelastic transducer as shown in FIGS. This type of transducer monitors mechanical probe speed rather than mechanical probe displacement. Both displacement-monitored and velocity-monitored transducers are non-linear with respect to drive frequency and typically show a distinct peak at the natural resonance frequency. This resonance frequency changes according to the viscoelastic properties of the fluid or gel to be measured. This peak is present in the examples shown in FIGS. Viscoelastic transducers vary widely depending on their design. One variation relates to the direction of the probe operation. Prior art designs incorporate axial, lateral, pivotal or radial probing of the transducer. An example of a conventional transducer that uses an axially oscillating probe is described in US Pat.
7,295 and 3,741,002 and Sim
No. 4,026,671 to On et al. U.S. Pat. No. 4,312,217 to Hartert and U.S. Pat. No. 4,341,111 to Husar use resilient rods that are driven to create a lateral or pivoting motion. Disclose that. U.S. Pat. No. 4,488,427 to Matusik et al. Teaches rotational or radial mechanical vibration. These prior art transducers incorporate a single flexible member that deforms to produce the desired mechanical movement. Simon and Si
The axially oscillating transducer taught by the Mon et al. patent incorporates a diaphragm. The lateral or pivoting movement taught by Hartert and Husar uses an elastic rod that is driven to bend the rod in one direction for lateral movement or two directions for pivoting movement. This is achieved by: Mut
The radial movement taught by asik occurs by using a resilient cylindrical tube that is driven using a torsional force that creates a radial bias. Most commonly used vibration transducers use separate drive and pickup coils. However, it is not necessary to use individual coils. The transducer taught by Simon et al. Uses a single coil at the same time to drive the transducer and also monitor mechanical operation.
The viscous or viscoelastic analyzer monitors the transducer response using appropriate circuitry and computational techniques to determine the viscous or viscoelastic properties of the material under test. Circuits for driving vibration transducers are well known in the art,
Typically, there is provided a drive circuit for generating a vibration mechanism operation and a monitor circuit for monitoring its mechanical movement. Additional circuits with means for adjusting the mechanical movement, monitoring the energy consumption or adjusting the signal for display are also taught in the prior art. Early designs drive the transducer at a fixed frequency. More advanced designs typically drive the transducer at the resonant frequency of the transducer immersed in the material to be measured. In advanced devices, the viscoelastic properties of the material being measured are determined by analyzing only the resonance point of the vibration transducer. The viscosity of the resonance peak characterizes the viscous properties of the test sample, while changes in frequency characterize its elastic properties. The accuracy of a viscosity and viscoelasticity measurement device incorporating a vibration transducer is limited by the operating characteristics of the vibration transducer. Prior art vibration transducers have poor manufacturing repeatability and vibration characteristics and tend to have temperature drift, long term drift and humidity drift. In addition, these transducers lack durability. Damage due to operator handling can cause either transducer drift or failure. In some designs, the transducer transfer coil is pressed against a magnet or pole, causing damage to the coil. In other designs, the transducer array is damaged by a few operator mishandling, thereby causing transducer drift or interfering with transducer vibration. Conventional transducers do not provide the necessary means of protecting oscillating mechanical components from excessively applied forces. While the Simon transducer vibrates axially, the diaphragm moves laterally or excessively axially while the operator monitors or removes the mechanical probe. As a result of this excessive movement, either the magnet or the magnetic poles come into contact with the coil, thereby damaging the coil. Approximately 95% of all requirements for this design are due to damaged coils. Further, the transducer characteristics tend to change when the diaphragm is pressed by excessive axial movement. To summarize the prior art, the vibration transducer taught in U.S. Pat. No. 4,341,111 to Husar relies on lateral or pivotal motion of an elastic rod. However, this does not provide a means to protect the elastic rod from being over-deformed. Matusi
The transducer taught in US Patent No. 4,488,427 to K et al. comprises a tube,
The tube is rotationally biased and the array of transducers must prevent the tube from laterally biasing. Similarly, the vibration transducers taught in U.S. Pat. Nos. 4,154,093 and 4,869,098 do not provide protection against excessive transducer displacement.

By providing mechanical stop means to limit the elastic deformation of the mechanical probe and to provide a generally rigid mechanical probe design except in the desired direction of elastic movement, operator handling is provided. The object is to provide a vibration transducer that minimizes damage.

SUMMARY OF THE INVENTION This and other objects are directed to an annular coaxially mounted mechanical probe to limit movement of a probe member in any direction other than the desired direction along the probe axis. This is achieved in accordance with a preferred embodiment of the present invention by providing a spring assembly and further by providing a mechanical stop to limit the extent of the desired direction along the probe axis.

DETAILED DESCRIPTION OF THE INVENTION The invention described herein is disclosed in U.S. Pat. Nos. 5,016,469 and 5,138,872.
And is incorporated herein by reference. The viscoelastic transducer of the present invention can be used, for example, in Henders
It can be used in place of the transducer described in US Pat. No. 5,016,469 to On.
Also, the viscoelastic transducer of the present invention can be used with the electronic circuit described in this patent specification. Figure 1
FIG. 4 shows a magnet cup portion 10, a permanent magnet 12, and a magnetic pole 14, which are positioned to create a uniform magnetic field in the gap between the permanent magnet 12 and the magnetic pole 14. Aligned and assembled with adhesive. The probe adapter hub 18 is bonded to both the inner ring 30 of the annular spring assembly 20 and the independent coil 16. The outer edge of the annular spring assembly 20 is aligned to position the coil 20 in the gap between the magnet 12 and the magnetic pole 14 and is adhered to the magnetic pole 14. The cover 10 is glued to the outer edge of the spring assembly 20 with an adhesive.
The mechanical probe moving within the transducer shown in FIGS. 1-4 comprises a probe adapter hub 18, a coil 16, a disposable probe 24, and an inner ring 30 of an annular spring assembly 20. Proper alignment during assembly allows the mechanical probe to move axially while maintaining clearance between the magnetic gaps. The coil 16 is used for driving a mechanical probe and detecting the movement of the probe. The typical characteristic response of the transducer of the present invention is shown in FIG. This transducer can be used with a variety of conventional control circuits, but in particular US Pat.
It is designed for use with the circuit described in 138,872. This circuit moves the transducer within the test sample at its resonant frequency. As the viscosity increases, the impedance of the transducer decreases. As the elasticity increases, the resonance frequency increases.
FIG. 5 illustrates the performance of this transducer in air, water, high mineral oil, and mineral oil gel. The characteristics of the viscosity of the test sample are characterized by how the resonance peak is attenuated. The elastic properties of the sample are characterized by a change in frequency. FIG. 4 shows an annular spring assembly 20 consisting of two annular springs 26 soldered to an inner ring 30 and an outer ring 28 made of brass. The two annular springs 26 are, for example, Glastonbury, Connecticut, USA.
ry) made from beryllium copper plates using conventional photochemical processing processes, such as those commercially available from Conard. The compliance of the two annular springs 26 can be changed by changing the length, width, or thickness of the spring web. Materials other than beryllium copper may be used. However, a preferred material is beryllium copper because of its excellent and stable spring properties. The annular spring assembly 20 is joined using lead-tin solder, but can also be joined by welding, brazing, or gluing. As described above, the annular spring assembly 20
Is constructed using two parallel springs 26 to provide the mechanical probe with lateral stiffness. Although the use of a single spring can provide excellent performance as a viscoelastic transducer, it does not provide the lateral stiffness that would prevent the coil 16 from being damaged during operator manipulation of attaching and detaching the disposable test probe. . Spring assembly 20 provides stiffness for movement in all directions except for axial displacement. Two or more annular springs 26 can be used, but in this case, the cost and complexity are increased.
The degree of improvement in mechanical stiffness that provides resistance to unnecessary mechanical bias is small. The mechanical design of the viscoelastic transducer of the present invention includes physical stops that limit the range of movement of the disposable mechanical probe 24. The magnet 12 limits the inward deflection and the cover 22 limits the outward deflection. These physical stops prevent the annular spring assembly 20 from being excessively deformed when the disposable probe 24 is attached and detached. With this design, movement of the probe adapter hub 18 from a normal position relative to either the magnet 12 or the cover 22 is approximately 0.254 mm (0.02 mm).
10 inches). The amount of this movement falls within the elastically biased operating region of the annular spring assembly 20. These stops, however, provide a range of movement of the mechanical probe 24 during normal test operation of about 0.2 mm.
At a distance much greater than 0508 mm (0.00020 inches). In short, the viscoelastic transducer of the present invention is a simple, reliable and accurate transducer for characterizing the viscous properties of a liquid or gel. Furthermore, with this transducer,
It incorporates a mechanism that increases the transducer's resistance to undesired mechanical stress and limits the mechanical bias of the transducer within the elastic operating limits of the spring member, which is superior to the prior art.
This design also increases the compliance of the spring assembly 20 without sacrificing durability. Such high spring compliance is desirable to increase the sensitivity of the transducer to weak gels. While the embodiments of the transducer of the present invention have been described in terms of an axially moving design, the transducer of the present invention provides for radial, lateral, pivotal, or any other type of vibration. Can be designed to An embodiment has been described in which the transducer of the present invention uses one coil for both mechanical drive and motion pickup purposes. However, separate coils can be used for each application. Additional coils or other means may be incorporated to allow for greater movement. In a pivoting design, multiple coils for driving and multiple coils for pickup may be used. The drive and pickup devices are not limited to coils. Other voltage-based methods include Hall effect, capacitive, piezoelectric, or other forms of electromechanical energy conversion or detection. Finally, an embodiment of the transducer of the present invention has been described using two flat shaped annular springs to allow the desired mechanical movement of the oscillating mechanical component.
The invention is not limited to designs using flat shaped annular springs. Many forms of elastic members, including but not limited to coil springs, elastic tubes, biasing rods, or wires, can be used as elastic members for mechanical vibration. Furthermore, if another mechanical vibration is realized by mechanical or elastic means, no mechanical elastic member is required for the mechanical vibration.

By providing mechanical stop means for limiting the elastic deformation of the mechanical probe and providing a generally rigid mechanical probe design except in the desired direction of elastic movement, the transducer is operated by the operator. The damage caused by the handling of the sheet can be minimized.

[Brief description of the drawings]

FIG. 1 is a perspective view of a viscoelastic transducer constructed in accordance with the present invention.

FIG. 2 is a cross-sectional view of the viscoelastic transducer of FIG.

FIG. 3 is an exploded view of the viscoelastic transducer of FIGS. 1 and 2;

FIG. 4 is an exploded view of an annular spring assembly used in the viscoelastic transducer of FIGS. 1-3.

FIG. 5 is a graph showing a relationship between a driving frequency and a mechanical probe displacement in the viscoelastic transducer of FIGS. 1 to 4;

FIG. 6 is a graph showing a relationship between a driving frequency and a mechanical probe speed in the viscoelastic transducer of FIGS. 1 to 4;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Magnet cup part 12 Permanent magnet 14 Magnetic pole 16 Independent coil 18 Probe adapter hub 20 Ring spring assembly 22 Cover 24 Disposable probe 26 Ring spring 28 Outer ring 30 Inner ring

Claims (10)

[Claims] 1. A transducer for use in a viscosity analyzer of the type in which a mechanical probe member is immersed in a liquid or gel whose viscosity properties are required, said probe member being driven to give a desired vibration. And a movement limiting means for limiting movement of the probe member in an arbitrary direction other than a desired vibration direction. 2. The transducer of claim 1 wherein said motion limiting means includes mechanical stop means for limiting deflection of the probe member in a desired direction of vibration. 3. The transducer of claim 1, wherein said probe member includes a disposable element and a non-disposable element. 4. The movement limiting means includes an annular spring assembly coupled to the probe member for limiting movement of the probe member in all directions except a direction along an axis of the probe member. The transducer according to claim 1, wherein: 5. The transducer according to claim 4, wherein the annular spring assembly includes a pair of annular springs spaced apart from each other and coaxially coupled at their outer edges to an annular ring. 6. The transducer of claim 5, wherein each of said annular springs includes a beryllium copper annular ring. 7. A transducer for use in a viscosity analyzer of the type in which a mechanical probe member is immersed in a liquid or gel whose viscosity properties are required and said probe member is driven to give a desired vibration. And a stop means for limiting the deflection of the probe member in a desired direction of vibration. 8. The transducer according to claim 7, wherein said probe member includes a disposable element and a non-disposable element. 9. The transducer according to claim 7, wherein said stopping means includes a combination of a cover member and a magnet. 10. The transducer according to claim 2, wherein said stopping means includes a combination of a cover member and a magnet.