IE46084B1 - Apparatus for measuring thickness of a layer - Google Patents

Description

This invention relates to apparatus for measuring the thickness of a layer, for example, fat thickness of pig carcasses.

The apparatus of the present invention is intended primarily for Use on pig slaughterhouse conveyor lines to give an automatic readout . of the thickness of fat at a pre-determined point on each carcass. In this respect it is designed to replace the use of an optical probe in which a probe is adjusted by the operator until the fat/muscle interface is observed to coincide with a cross-wire in the optical system. In this known probe the fat thickness is then read off on a circular scale and usually marked on the carcass for later transmission into the factory's data acquisition system by a second operator at a keyboard. The apparatus of the present invention relies on a light souree/photocell combination to automatically detect the interface between fat and muscle layers. Using logic circuitry and a simple resistive distance transducer, a digital readout of the fat thickness in millimetres is displayed on the hand held probe unit and on the control unit. According to the present invention there is provided apparatus for measuring the thickness of a layer comprising a probe including means for detecting a fat layer/lean meat interface in a carcass; means providing a signal representative of the depth of insertion of the probe into the carcass from a datum position; and electronic circuit to read said signal when said fat layer/ lean meat interface is detected; and means for displaying or storing said read signal. -2Preferably, said means for detecting includes a light source and a photo-diode.

Preferably also,said signal providing means is a rectilinear potentiometer mounted parallel to said probe.

An embodiment of the present invention will now be described by way of example with reference to the accompanying drawings, in which:Fig. 1 is a perspective view of a probe unit forming part of the apparatus according to the present invention; Fig. 2 is a detail view of part of the probe unit of Fig, 1; Fig. 3 is a sectional view, to an enlarged scale, through the line III-III of Fig.2; Fig. 4 is a block diagram of the electronic circuitry used; and Fig. 5 is a perspective view of one embodiment of apparatus made in accordance with the present invention: Referring to the drawings, apparatus for measuring the thickness of a layer Includes a hand-held probe assembly 1 which includes a stainless steel probe 10 with a cutting tip 11 for insertion into a carcass. On the shaft of the probe 10 a longitudinal slit shaped window 12 is provided behind which is mounted a low voltage filament light source 13 and a minature photodiode light detector 14, separated from the light source 13 1 by a light mask 16. Mounted with its moving shaft 15a parallel to the axis of the probe 10 is a resistive linear displacement transducer in the form of a rectilinear potentiometer 15 (Fig. 4). The output - 3 . 4 6 0 8 4 from the transducer 15 is a low voltage, the magnitude of which is proportional to the shaft displacement.

A finger operated trigger switch 17 is mounted in the hand grip 18 of the probe assembly 1 and a two digit light emitting diode display unit 19 is mounted behind the sloping panel towards the rear of the probe assembly.

As can be seen from Fig. 5, the probe assembly 1 is connected to a control unit 2 by a length of multi-way cable 3. The control unit 2 contains the main power supplies 20 and control electronics 21. On the front panel of the control unit 2 there is provided an on/off switch 28 and digital voltm^er display 29. The rear panel of the uiit2 contains the connections to the mains electricity supply, the probe assembly 1 and the particular interface unit (if automatic transmission of data is required).

The sequence of operations is as follows: (i) The operator inserts the probe 10 of the probe assembly 1 into the carcass, ensuring that the probe tip 11 and optical window 12 have penetrated t into the red muscle tissue, (ii) The trigger 17 is operated and the probe 10 steadily withdrawn from the carcass. As the optical window 12 crosses the muscle/fat interface the actual fat depth in millimetres appears on the digital displays 19 and 29 on both the probe assembly 1 and control unit 2. (iii) After recording the indicated fat depth the trigger 17 is released to re-set the apparatus for the next measurement.

An additional interface unit may be included between the control unit and the factory's data acquisition system -to allow.the information.to be automatically recorded on command from the data acquisition system. The - 4 - : 6 0 8 4 detailed design of this interface unit of course depends on the specification of the particular data acquisition system in use.

If such an interface unit for automatic data recording is fitted the operation is as (i) and (ii) above. The trigger 17 is held in the 'operate ' position until the probe assembly display 19 automatically blanks. This indicates that the data acquisition system has recorded the reading. The automatic recording does not take place until a variable preset delay time (0-10 seconds) has expired. This enables the operator to cancel the reading and re-probe the carcass if necessary.

The linear displacement transducer 15 has a 75 mm stroke length and is scaled to read zero volts with the probe withdrawn and to read 0. 75 volts with the probe inserted to its full extent. The output from the transducer is fed directly to the digital voltmeter and display 29 which will, on command, display the transducer output signal as a two digit 15number between zero and 75, Thus indicating the shaft position of the transducer in millimetres.

The probe light source 13 is a sub-miniature lamp operated continuously from a 5 volt supply and a PIN photodiode is used as the light detector 14.

The relative positions of the light source 13 and light detector 14 are clearly 20 seen in Fig. 2 and 3.

When the probe 10 is inserted into the muscle the light is diffused and scattered within the muscle tissues, some finding its way back to the light detector 14 as indicated in Fig. 3, The signal developed across the load resistor of the photodiode is proportional to the light transmission 25 properties of the muscle tissue and this signal is fed by way of an adjustable gain - 5 amplifier 22 (Fig. 4) with an offset control 23 to the input of a track and hold anplifier 24. High frequency filtering is provided at the input to the track and hold amplifier 24 to remove any spurious signals generated by nearby factory machinery. The output of the track and hold amplifier 24 is divided by 10 in divider 25 and fed to the inverting input of a comparator/switch circuit 26.

When the probe trigger 17 is operated, read/reset line 33 raised to logic high which has the effect of placing the track and hold amplifier 24 in the hold mode thus 'remembering' the light scattering signal from the muscle tissue. The photodiode signal is additionally coupled to a level detector circuit 27 and by way of an adjustable divider circuit 34 to the non-inverting input of the comparator/switch circuit 26, As the probe 10 is withdrawn from the carcass and the optical window 12 crosses the muscle/fat interface the photodiode signal increases by a factor of approximately 2. The adjustable divider circuit 34 is typically set to divide by 15. Thus, when the photodiode signal increases to a value 1. 5 times greater than the original 'remembered' signal at the track and hold amplifier 24, the output from the comparator 26 is driven positive and a logic high level is fed to the B input of an AND gate circuit 30. Input A of the gate circuit 30 is already at high level via the read/reset line 33, The 'AND' gate 30 closes providing a logic high level to a clock input on a latch circuit 31. The latch circuit 31 in turn provides a read and hold signal to a digital voltmeter 32. The latch circuit 31 will retain its output to the digital voltmeter 32 and ignores any further clock pulses until the trigger 17 is released to reset the latch circuit 31. The digital voltmeter 32 therefore performs a single conversion and records the instantaneous output (position) on the control unit display 29. Parallel information is supplied to the digital display 19 on the probe assembly 1.

When the trigger 17 is released the read/.reset-line 33 is returned to logic 6 0 8 4 low level thus resetting the logic latch circuit 31 and digital voltmeter 32, at the same time returning the track and hold amplifier 24 to the tracking mode.

When used in conjunction with an interface unit for automatic data 5 transmission, the trigger 17 is held in the operate position until a blanking signal is returned via the control unit 2 to the probe assembly display 19 to indicate that the data has been recorded. The unit is then ready for a further measurement.

Claims (5)

CLAIMS:

1. Apparatus for measuring the thickness of a'layer comprising a probe including means for detecting a fat layer/lean meat interface in a carcass; means providing a signal representative of the depth of insertion of the probe into the carcass from a datum position; and electronic circuit to read 5 said signal when said fat layer/lean meat interface is detected; and means for displaying or storing said read signal,

2. Apparatus as claimed in Claim 1 wherein said means for delecting includes a light source and a photodiode,

3. Apparatus as claimed in either Claim 1 or 2 wherein said signal providing j_q means is a rectilinear potentiometer mounted parallel to said probe.

4. Apparatus as claimed in any preceding Claim wherein said probe, detecting means and said signal providing means are located in a single probe head assembly.

5. Apparatus for measuring the thickness of a layer substantially as 15 hereinbefore described with reference to the accompanying dravzings. - 3 4 6 0 8 4 Dated this the 14th day of November, 1977. F. R BY: KELLY & CO. , EXECUTIVE. 27 Clyde Road, Baiisbridge, Dublin 4. AGENTS FOR THETAPPLICANTS. PIGS MARKETING BOARD (NORTHERN IRELAND) 46 08 4