WO1987005462A2

WO1987005462A2 - Apparatus for determining meat quality

Info

Publication number: WO1987005462A2
Application number: PCT/DK1987/000100
Authority: WO
Inventors: Svend T. Olesen
Original assignee: Slagteriernes Forskningsinstitut
Priority date: 1987-06-30
Filing date: 1987-08-13
Publication date: 1987-09-24
Also published as: WO1987005462A3; DK154363B; DK334087D0; DK154363C; DK334087A

Abstract

An apparatus for determining the quality of meat comprising a probe (1) to be inserted into a piece of meat which is to be examined and reflection measuring means placed in the probe having a light emitter (2) and a light receiver (3). A reference light receiver (4) which controls the supply to the light emitter (2) is placed in the probe near the light emitter. The servo link formed will compensate for the fluctuating efficiency of the light emitter (2) and the light receiver (3). The intensity of the light emitter may automatically be kept at a constant level.

Description

Apparatus for determining meat quality

The present invention relates to an apparatus for determining meat quality, comprising a probe for insertion into meat material which is to be examined and reflection measuring means arranged in the said probe, having a light emitter and a light receiver.

In order to comply with consumer wishes for meat of uniform and high quality modern slaughterhouses perform an objective quality determination of pigs after slaughtering. A measuring device comprising an insertion probe and means for measuring the insertion depth is applied to determine the thicknesses of meat and fat of the individual pig carcasses. The probe is inserted at a number of places on each carcass, and the thicknesses measured are used together with the weight of the carcass to determine the grading of the carcass.

In the US patent No. 4,439,037 and 4,352,245 are description of such apparatuses for the determination of the thicknesses of meat and fat in carcasses. These apparatuses comprise a probe with reflection measuring means which registers the reflective power of the material situated outside a window on the side of the probe. These apparatuses utilize the fact that meat and fat are of different reflective power.

It is well known that there is a certain correlation between the colour of the meat and its quality. In certain cases very pale pork may for instance have a poor power of water absorption, and consequently it appears to be dry to the consumer. There is also a tendency of consumers considering pale meat less valuable than heavily pigmented meat.

By means of various measures the pig breeders and slaughterhouses try to reduce the incidence of pale meat, but so far the efforts have been complicated by a lack of objective determination of the relationship between quality and the measured colour of the meat. Apparatuses are known which can indicate the colour or reflective power of the meat, but the values obtained are not sufficiently reliable for laying down any generally applicable, objective quality criterion for meat based upon such colour measurements.

US patent No. 3,493,774 describes an apparatus for determining the quality of meat based upon colour measurement. The apparatus is provided with an insertion probe with a window. Immediately in front of this window there is an incandescent lamp which will illuminate the meat. The light being reflected from the meat is sent through the window via a mirror placed in the probe to a photo cell in the apparatus itself. This photo cell is connected with a deflection instrument, the deflection of which indicates the power of the meat to reflect light or its colour intensity.

In a paper presented at the 21st European Meeting of Meat Research Workers, 31st August to 5th September 1975, p. 114-115 is a description of another apparatus for the determination of meat colour. The apparatus is provided with a fibre-optical probe intended for insertion into the meat. A bundle of fibres leads from an incandescent lamp to the tip of the probe. Another bundle of fibres, running parallel to the first bundle, transmits the reflected light from the tip of the probe to a photo transistor. This transistor is connected with a deflection instrument showing the colour intensity.

Neither of these apparatuses nor the apparatuses known from the above mentioned US patents No. 4,439,037 and 4,352,245 provide sufficiently reliable results as regards the measured colour of the meat. They cannot be used as a basis instrument for a measuring system which shall be able on a general basis and in an objective way to distinguish meat with different characteristics of colour. An object of the present invention is to provide a measuring apparatus by means of which it is possible to obtain results from measurements of the reflective power of meat which are more reliable than the ones obtained so far. In particular, it is the object to provide an apparatus, the readings of which are less sensitive to changing working temperature more uniform from one apparatus to another, and less influenced by the phenomena occurring in light emitter and light receiver due to age.

According to the present invention there is provided an apparatus for determining meat quality, which apparatus comprises a reference light receiver placed in the probe.

By using a reference light receiver it is possible to compensate for the varying efficiency of the light emitter and/or light receiver. This varying efficiency may for instance be due to variations which can be traced back to varying conditions of manufacture for the probe or its components, differences between the temperature of the carcass and the room temperature of the slaughterhouse, or changes in the properties of the components as a result of ageing in general.

The reference light receiver may for instance be placed near the light emitter in such a way that it will receive light from the light emitter, either directly or via a mirror. In this way it is possible to control the light emitter by means of its own light emission. The apparatus of the invention may comprise a regulator connected with the reference light receiver, said regulator controlling the supply to the light emitter. The supply may for instance be a current source which is regulated by a signal received from the reference light receiver.

The regulator may be constructed in such a way that the signal of the reference light receiver is essentially kept constant. In this way the light intensity from the light emitter is essentially kept at a constant level.

The regulator will turn up the light emitter if the light intensity is under the prescribed level, for instance if the emitter happens to be one of those components of a production which deviates from the ideal value but nevertheless is within the limits of tolerance. The regulator will similarly turn down the light emitter if the light intensity is above the prescribed level, for instance if the working temperature is lower than prescribed.

The regulator may comprise an adjustable amplifier which is connected with the control input of the supply. In this way it is possible to adjust the light intensity of the light emitter at the desired working level.

The apparatus according to the invention shows great stability in the results of the measurements over longer periods of time without any need for calibrations, as the reflection measuring means of the apparatus will automatically adjust itself to the changed conditions.

According to one embodiment of the invention the supply of the light emitter is modulated, especially with a square wave signal. This makes it possible to distinguish between the light from the light emitter and signals coming from other sources. This may for instance be false light or undesirable, non-load current.

According to the mentioned embodiment, the regulator may comprise a synchronous detector which preferably works at a frequency which is twice as high as the modulation frequency of the supply. In this way only the signal which has relation to the light emitted by the light emitter will be detected. The said double frequency makes it possible to eliminate the first quarter period of the signal of the reference light receiver, which often has undesirable voltage transients because of signal coupling between the components.

In order to increase the signal variation interval of the system there is mainly at least one AC-coupling in the signal path of the regulator.

The signal supplied by the light receiver may be set at a predetermined value corresponding to a certain light reflection. The apparatus will thus be able to meet a common standard which gives comparable results of measurement. In accordance with this, the apparatus of the invention may comprise an adjustable amplifier for the light receiver.

Several apparatuses according to the invention may be adjusted to a common standard by means of a material having well defined reflective power. Each apparatus may be adjusted to a certain working level, while the probe is placed in a calibration ball or a similar material with constant reflective power, for instance a suspension such as milk. By the reference given the apparatuses are adjusted one after another whereby the results obtained from the measurements are related to the common standard.

In order to increase the overload capacity a DC-regulating feedback may be provided in the amplifier for the light receiver. This is particularly advantageous when the light emitter is modulated, as false light and bias signals are eliminated from the signal of measurement. The DC-regulating feedback gives a considerably more accurate signal of measurement than an ordinary AC-coupling.

The light receiver may be optically separated from the light emitter by means of a small partition wall in the probe. Nevertheless, for mechanical reasons it cannot be prevented that a little light is scattered from the light emitter to the light receiver, which is particularly unfortunate in dark surroundings. This contribution to the signal of measurement in the light receiver can be compensated for by means of a summation amplifier for the light receiver. One input terminal of the amplifier is supplied with the signal originating from the light receiver, and the other input terminal is supplied with a constant, but adjustable signal. On calibration the latter signal will reduce to zero, the signal originating from said light being scattered. When the supply of the light emitter is modulated, the amplifier for the light receiver may comprise a synchronous detector, which especially works at a frequence twice as high as the modulation frequency of the supply. In this way that part of the signal which originates from false light or non-load current can be eliminated. When the double frequency is being used it is possible to eliminate the first quarter period of the signal of measurement, which often includes undesirable voltage transients. This improves the accuracy of the signal of measurement.

The apparatus according to the invention may comprise devices for amplifying and processing the signal being generated in the light receiver. Thus, the apparatus may comprise a analogue/digital converter to change the signal from the light receiver into binary values.

In this way a number of successive measurements can be made and the results may be stored in a memory for later processing in a computer programme.

The thicknesses of meat and fat are determined by insertion (and extraction) of the probe of the apparatus in a piece of meat. By the same measurement one might also determine whether the meat is of deviating quality, viz. if one or several of the stored and registered measurements exceed a predetermined threshold limit. Low quality meat may be very light or contain fatty tissue. On the basis of the results pieces of low quality meat can be sorted out. On the basis of the results obtained one might also establish a system which will sort out pieces of meat of particularly high quality.

If one or several of the results obtained by the insertion is/are not in accordance with what may be expected from experience, these measurements may automatically be left out, or a signal may be produced indicating that the measurement by insertion should be repeated. The apparatus according to the invention may thus comprise a data processing unit to convert the signals of the light receiver into quality gradings of the piece of meat being measured, and a recording instrument to store the quality gradings. The functions of the data processing unit are determined by the task at hand.

The unit may be arranged in such a way that it will store the measurements from a number of insertions on the same piece of meat, and on the basis of the processed results it will operate a grading and stamping system which will provide for the piece of meat to be used in accordance with the ascertained grade of quality.

The apparatus according to the invention may comprise a device for successive registration of the movement of the probe during insertion. A signal disclosing the location of the probe, for instance whether it is in the outermost or innermost postion, may be provided in automatic systems. The device may comprise switches which are activated in these positions, but it may also include a length indicator what currently reports the actual position of the probe in the form of a positional value. In our Danish patent application No. 4247/86 is a description of a length indicator in a automatic probe unit intended for fixing in a rest or on a sliding bracket.

The apparatus according to the invention may comprise a device for successive registration of the depth of insertion of the probe into a piece of meat. It may be the type of depth measuring devices which is known from the manually operated instruments for measuring thicknesses of meat and fat. These measuring devices are provided with a plate which lies true against the surface of the carcass while the probe is inserted into the carcass. The measuring devices are provided with an exchange mechanism between the plate and the probe which will convert the actual depth of insertion into an electric signal.

The reference light receiver of the invention may be of the same type as the light receiver used in the apparatus, as the receiver often will have operating characteristics which are much alike. Deviations in the reference light receiver and in the light receiver will often be compensatory. A light emitting diode may be used as a light emitter, whereas a photo diode or photo transistor may be used as a light receiver. These components are so small that they may be placed in a thin probe, and they have a suitably long life.

In order to compensate for faults arising because of fluctuations in temperature, the semi-conductors mentioned may be mounted on the same substratum, preferably a ceramic plate.

The light emitter, the light receiver and the reference light receiver may all be placed in the probe, but it is also possible to place them in tne housing which usually carries the insertion probe, for instance by using optical fibres which will conduct the light to and/or from the place of measurement in the probe.

The probe may be provided with a window on the side, through which light may be emitted and received. This will keep the place of measurement in the probe free from impurities which are detached during the insertion of the probe into the piece of meat.

The light emitter, the light receiver and the reference light receiver may be embedded in the probe in a transparent epoxy resin. In this way they will remain at the same intervals all through their life, and it becomes easier to perform the adjustment of the electric circuit according to their characteristics.

The invention also relates to a probe to be used in an apparatus for determining the quality of meat comprising reflection measuring means arranged in this probe having a light emitter and a light receiver. The probe according to the invention comprises a reference light receiver placed in the probe. The invention also relates to a circuit to be used in an apparatus for determining the quality of meat comprising a supply to a light emitter and a measuring device for a light receiver. The circuit according to the invention comprises a regulator which controls the supply to the light emitter, said regulator controlling the supply dependent on an external signal applied to the input terminal of the regulator.

The invention is described in detail below, with reference to the drawing which shows a probe and a circuit in an apparatus for determining the quality of meat.

In a probe 1 is placed a light emitting diode 2, a photo sensitive diode 3 and a reference photo sensitive diode 4 on a common ceramic plate. Part of the light emitted by the diode 2 is reflected in a mirror 5 and is sent down upon the reference diode 4. Another part of the light emitted by the diode 2 is sent through a window 6 which is located on the side of the probe. When the probe 1 is inserted into meat material, the meat which is just outside the window 6 will reflect or scatter part of the light back through the window to the diode 3. The degree of reflection will depend, among other things, upon the colour intensity of the meat (fatty tissue, dark meat and light meat will give different reflections).

A wall 7 prevents the light of diode 2 from being applied directly to the photo diode 3. The wall, the mirror and the plate with the diodes are embedded into the probe in a transparent plastic such as epoxy resin.

The distances between the diodes are essentially such that the light has to travel the same distance from the diode 2 to the diode 4 as from the diode 2 via the main reflection beam to the diode 3. Furthermore, the distances, the mirror and the wall are of such dimensions that the in tensity of the light which is applied to the diode 3 by reflection is of the same order of magnitude as the intensity of the light being applied to the diode 4. The three diodes are connected via wires in the probe with a circuit, the most essential elements of which are shown on the drawing. It includes a supply for the diode 2, a regulator for the said supply which is connected with the reference photo diode 4, and a measuring device which will convert the signal of the photo diode 3 into a result of measurement.

The supply is controlled by a regulator transistor 8. To the basis of the transistor is applied a voltage which determines the current of the supply. The voltage is applied via a wire 9 as described further below.

The current to the diode 2 may be shunted by means of a switch transistor 10, so that the light emission of the diode 2 varies when a control signal is applied to the transistor 10. Via an inverter 12 a timing circuit 11 delivers a harmonically varying impulse as a control signal. This signal is a square wave signal with a frequency of 4 kHz. The components 10, 11 and 12 thus handle the modulation of the light diode 2.

The diodes 13 and the resistor 14 prevent saturation of the shunt transistor 10, which will ensure a 50% duty cycle.

The diode 15 and the resistor 16 will ensure that a low bias current always flows in the light diode 2. This will reduce the voltage swing over the light diode, which gives less problems with the stray capacitance from the supply lines to the sensor components of the probe.

The regulator for the supply of the light diode includes a pre-amplifier 20 for the reference photo diode 4. A coupling capacitor 21 removes the DC-part of the diode signal. By means of a potentiometer 22, the signal level is adjusted and in doing so the feedback of the regulator. The setting of the potentiometer 22 will determine the light intensity of the light diode 2. The level-adjusted reference signal will be amplified in a pre-amplifier 23 and a buffer 24 is provided allowing the use of fairly long cables to a subsequent synchronous switch 25. The switch is operated by a square wave generator 26 with a frequency of 8 kHz.

The switch 25 eliminates the first quarter periods of the square wave signal on the output of the buffer 24. However, the switch allows the last quarter periods of the signal to pass and these signals are integrated and held in resistors 27 and capacitors 28 placed in the input terminals of a differential amplifier 29.

In an amplifier 30 the output signal from the differential amplifier 29 is compared with a set reference voltage. Via the wire 9 the signal obtained is applied to the regulating input terminal of the light diode's supply, i.e. the basis of the transistor 8.

The reference signal which is detected and processed in the described regulator will control the supply to the light diode 2, dependent on the intensity of light which falls on the photo diode 4. The servo link provided will try to keep the current of the diode 4 constant.

The measuring circuit which converts the signal of the photo diode 3 into a result of measurement has several things in common with the regulator curcuit described above. In an amplifier 40 the current of the diode is converted into a voltage, which is amplified in the amplifier 41. The DC-part of the signal is removed by means of a feedback 42, which forms a local DC servo link together with the amplifiers 40 and 41. As a result, the amplifiers will not be overloaded if the diode 3 is illuminated with intense external light, such as sunlight or electric light.

The level of the diode signal may be set with a potentiometer 43 and in this way several instruments may be calibrated to show the same result of measurement at a given colour intensity. Via an amplifier 44 the signal is conducted to one input of a summation amplifier 45 with two input terminals. The other input terminal is connected with a potentiometer 46, which may be set in such a way that undesirable coupling of light to the photo diode 3 and electric stray coupling are compensated for. At the same time the amplifier 45 serves as an output buffer.

The signal is conducted to a synchronous switch 47, which is controlled by the above mentioned square wave generator 26. The chopper frequency of the light diode 2 and the timing of the gate signal of the synchronous switch are selected in order to obtain immunity to power-line hum and external light signals which has not been filcered off. This makes it possible to perform measurements of meat quality in the premises of work at the slaughterhouses.

A differential amplifier 48 with two R-C circuits 49, 50 in the inputs will detect the signals on the output of the switch 47 in the same way as for the switch 25. The amplified and synchronously detected signal is filtered in an active low-pass filter 51. The s.noothed signal is digitized in an analogue-to-digital converter 52.

The digitized signal which is expressive of the colour intensity of the meat, may be shown direct on a display or it may be subjected to data processing.

As the servo link in question keeps the light emission of the light diode 2 constant and as the two photo diodes 3 and 4 are alike and kept at the same temperature, the instrument may be used to measure light reflection, independent of temperature, ageing of the components and external light. This is essential when the quality of meat is to be measured on-line at slaughterhouses.

Claims

C l a i m s

1. Apparatus for determining meat quality, comprising a probe (1) for insertion into meat material, which is to be examined and reflection measuring means arranged in this probe having a light emitter (2) and a light receiver (3), c h a r a c t e r i z e d in that a reference light receiver (4) is placed in the probe.

2. Apparatus according to Claim 1, c h a r a c t e r i z e d in that a regulator is connected with the reference light receiver (4), said regulator controlling the supply to the light emitter.

3. Apparatus according to Claim 2, c h a r a c t e r i z e d in that the regulator is constructed in such a way that the signal of the reference light receiver (4) is essentially kept constant.

4. Apparatus according to Claims 1-3, c ha r ac t e r i z e d in that the supply of the light emitter is modulated, especially with a square wave signal (11).

5. Apparatus according to Claim 4, c h a r a c t e r i z e d in that the regulator comprises a synchronous detector (25) which preferably works at a frequency which is twice as high as the modulation frequency of the supply.

6. Apparatus according to Claim 4, c h ar ac t e r i z e d in that an amplifier for the light receiver (3) comprises a synchronous detector (47) which especially works at a frequency which is twice as high as the modulation frequency of the supply.

7. Probe to be used in an apparatus for determining meat quality, comprising reflection measuring means arranged in this probe having a light emitter (2) and a light receiver (3), c h a r a c t e r i z e d in that a reference light receiver (4) is placed in the probe.

8. Circuit to be used in an apparatus for determining meat quality, comprising a supply to a light emitter (2) and a measuring device for a light receiver (3), c h a r a c t e r i z e d in a regulator which controls the supply to the light emitter (2), said regulator controlling the supply dependent on an external signal applied to the input terminal of the regulator.

9. Circuit according to Claim 8, c h a r a c t e r i z e d in that the supply of the light emitter (2) is modulated, especially with a square wave signal (11).

10. Circuit according to Claim 9, c h a r a c t e r i z e d in that the regulator comprises a synchronous detector (25) which preferably works at a frequency which is twice as high as the modulation frequency of the light emitter.

11. Circuit according to Claims 9-10, c h a r a c t e r i z e d in that an amplifier for the light receiver (3) comprises a synchronous detector (47) which especially works at a frequency which is twice as high as the modulation frequency of the light emitter.