GB2167568A

GB2167568A - Method and apparatus for the measurement of the hardness of compliant materials

Info

Publication number: GB2167568A
Application number: GB08528780A
Authority: GB
Inventors: Eric Dransfield
Original assignee: Individual
Current assignee: Individual
Priority date: 1984-11-22
Filing date: 1985-11-22
Publication date: 1986-05-29
Also published as: GB8528780D0; GB8429550D0

Abstract

Apparatus for measuring the hardness of a compliant substance such as meat has a probe head 27 biased by a spring 24 and coupled to a linear displacement transducer 22. The body of the apparatus has a reference surface which is placed against the surface of the substance under test. Various exchangeable probe heads 27 e.g. conical, hemispherical, inverted cones, may be provided. The spring 24 may also be exchanged. <IMAGE>

Description

SPECIFICATION Method and apparatus for the measurement of the hardness of compliant materials The invention relates to the measurement of the hardness of compliant and viscoelastic materials and, in particular, to the measurement of the firmness of fatty tissues.

A criterion for assessment of meat in the slaughterhouse and elsewhere is the firmness or resistance to applied pressure. Subjectively, meat has been tested by applying pressure with the thumb to derive an indication of quality. Such methods are clearly operator-dependent and cannot be used as a basis for a standard quality specification.

One instrument, which seeks to eliminate the subjective influence of inspectors assessing rubber-like materials is the Durometer disclosed in US Patent 3136153, which is a form of clock gauge with a dial coupled to a spring-loaded projecting probe arm.

Unfortunately, the measurement using this mechanical instrument is sensitive to its orientation and consistent measurement can only be taken with the surface-under-test in a horizontal position.

Also, when used on fatty tissue, variable results were obtained because the reading changes with time after application. We have therefore devised a method of measurement which overcomes these problems and is therefore particularly advantageous for use with viscoelastic materials such as foods.

According to the present invention, there is provided apparatus for measuring the hardness of a compliant substance comprising probe means having a probe head to contact a surface of the compliant substance, actuator means to urge said probe head into contact with said surface of the compliant substance and electrical transducer means to measure the displacement of said probe head from a reference position.

The invention will now be particularly described with reference to the accompanying drawings, in which :- Figure 1 is a diagram representing components of measuring apparatus according to one embodiment of the invention.

Figures 2a-d are graphical representations of measurements taken using the apparatus of Figure 1.

Figure 3a is a section through the probe of Fig ure 3a; and Figure 4 is a representation of a number of probe heads of different shapes for use with the probe of Figure 3.

In one specific embodiment, a demountable probe head 1 is attached to the magnetic core 2 of a displacement transducer 3. The core is movable in the direction M within sensing coils 4 and an exciter coil 5 which is coupled to an oscillator 6 fed from a d.c. supply 7. The magnetic core is urged towards a reference position by a demountable, calibrated spring 8 held by an adjustable end stop 9. Different springs and probes may be employed for the measurement of different materials.

The output of the sensing coils 4 is fed to a demodulator 10 which is, in turn, coupled via a voltage conditioning and timing circuit 11 to a data storage and analysis circuit 12 and a display 13.

A reproducible relationship for the dependence of penetration on hardness has been found to exist, typical curves being shown for pork shoulder fat (Figures 2a, 2b, 2c) and agar gels (Figure 2d).

In a practical embodiment, (Figures 3a, 3b) the measuring apparatus comprises a body 20 with detachable handle section 21. Mounted within the body is a displacement transducer 22 having a movable magnetic core 23. An interchangeable calibrated spring 24 is held in place by a screwmounted lock unit 25 in order to apply variable pre-tensioning of the spring. An extension member 26 is screw-mounted on the core and, in turn, carries a demountable probe head 27. Surrounding the core extension is a demountable cover plate 28 which provides a reference surface 29 from which the probe head 17 protrudes. A cable 30 carries the signal to and from the transducer 22. Normally the area of the cover plate in contact with the material would be large but access to carcass backfat is restricted and the cover plate is shown small.A screw adjustment 31 is provided to position the linear transducer and probe protrusion precisely.

For general purpose measurements an inverted conical flat-ended probe head 40, 41 (Figure 4a, 4b) is suitable, whilst for other applications a hemisphere 4c or hemisphere with shoulders 4d or a cone 4e or double cone 4f is preferred. The optimum diameter of the probe head is dependent on the hardness of the compliant material to be measured.

1. Apparatus for measuring the hardness of a compliant substance comprising probe means having a probe head to contact a surface of the compliant substance, actuator means to urge said probe head into contact with said surface of the compliant substance and electrical transducer means to measure the displacement of said probe head from a reference position.

2. Apparatus for measuring the hardness of a compliant substance as claimed in Claim 1, further including a reference surface adjacent to said probe head wherein said probe head protruded beyond said reference surface when in its rest position.

3. Apparatus for measuring the hardness of a compliant material as claimed in Claim 2 wherein said reference surface encloses an aperture from which said probe head protrudes when in the rest position.

4. Apparatus for measuring the hardness of a compliant material as claimed in any one of the preceding claims wherein said probe head is demountable.

5. Apparatus for measuring the hardness of a compliant material as claimed in any one of the preceding claims wherein the probe head is conical

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Method and apparatus for the measurement of the hardness of compliant materials The invention relates to the measurement of the hardness of compliant and viscoelastic materials and, in particular, to the measurement of the firmness of fatty tissues. A criterion for assessment of meat in the slaughterhouse and elsewhere is the firmness or resistance to applied pressure. Subjectively, meat has been tested by applying pressure with the thumb to derive an indication of quality. Such methods are clearly operator-dependent and cannot be used as a basis for a standard quality specification. One instrument, which seeks to eliminate the subjective influence of inspectors assessing rubber-like materials is the Durometer disclosed in US Patent 3136153, which is a form of clock gauge with a dial coupled to a spring-loaded projecting probe arm. Unfortunately, the measurement using this mechanical instrument is sensitive to its orientation and consistent measurement can only be taken with the surface-under-test in a horizontal position. Also, when used on fatty tissue, variable results were obtained because the reading changes with time after application. We have therefore devised a method of measurement which overcomes these problems and is therefore particularly advantageous for use with viscoelastic materials such as foods. According to the present invention, there is provided apparatus for measuring the hardness of a compliant substance comprising probe means having a probe head to contact a surface of the compliant substance, actuator means to urge said probe head into contact with said surface of the compliant substance and electrical transducer means to measure the displacement of said probe head from a reference position. The invention will now be particularly described with reference to the accompanying drawings, in which :- Figure 1 is a diagram representing components of measuring apparatus according to one embodiment of the invention. Figures 2a-d are graphical representations of measurements taken using the apparatus of Figure 1. Figure 3a is a section through the probe of Fig ure 3a; and Figure 4 is a representation of a number of probe heads of different shapes for use with the probe of Figure 3. In one specific embodiment, a demountable probe head 1 is attached to the magnetic core 2 of a displacement transducer 3. The core is movable in the direction M within sensing coils 4 and an exciter coil 5 which is coupled to an oscillator 6 fed from a d.c. supply 7. The magnetic core is urged towards a reference position by a demountable, calibrated spring 8 held by an adjustable end stop 9. Different springs and probes may be employed for the measurement of different materials. The output of the sensing coils 4 is fed to a demodulator 10 which is, in turn, coupled via a voltage conditioning and timing circuit 11 to a data storage and analysis circuit 12 and a display 13. A reproducible relationship for the dependence of penetration on hardness has been found to exist, typical curves being shown for pork shoulder fat (Figures 2a, 2b, 2c) and agar gels (Figure 2d). In a practical embodiment, (Figures 3a, 3b) the measuring apparatus comprises a body 20 with detachable handle section 21. Mounted within the body is a displacement transducer 22 having a movable magnetic core 23. An interchangeable calibrated spring 24 is held in place by a screwmounted lock unit 25 in order to apply variable pre-tensioning of the spring. An extension member 26 is screw-mounted on the core and, in turn, carries a demountable probe head 27. Surrounding the core extension is a demountable cover plate 28 which provides a reference surface 29 from which the probe head 17 protrudes. A cable 30 carries the signal to and from the transducer 22. Normally the area of the cover plate in contact with the material would be large but access to carcass backfat is restricted and the cover plate is shown small.A screw adjustment 31 is provided to position the linear transducer and probe protrusion precisely. For general purpose measurements an inverted conical flat-ended probe head 40, 41 (Figure 4a, 4b) is suitable, whilst for other applications a hemisphere 4c or hemisphere with shoulders 4d or a cone 4e or double cone 4f is preferred. The optimum diameter of the probe head is dependent on the hardness of the compliant material to be measured. CLAIMS

5. Apparatus for measuring the hardness of a compliant material as claimed in any one of the preceding claims wherein the probe head is conical in shape.

6. Apparatus for measuring the hardness of a compliant material as claimed in Claim 5 wherein the probe head is in the shape of a double cone.

7. Apparatus for measuring the hardness of a compliant material as claimed in Claim 5 wherein the probe head is in the form of an inverted cone.

8. Apparatus for measuring the hardness. of a compliant material as claimed in any one of Claims 1 to 4 wherein the probe head is substantially hemispherical in shape.

9. Apparatus for measuring the hardness of a compliant material as claimed in Claim 8 wherein the probe head is provided with a shoulder to reduce penetration.

10. Apparatus for measuring the hardness of a compliant material substantially as herein described with reference to and as shown in the accompanying drawings.