Data processing: measuring – calibrating – or testing – Measurement system in a specific environment – Mechanical measurement system
Reexamination Certificate
2002-11-18
2004-11-09
Hoff, Marc S. (Department: 2857)
Data processing: measuring, calibrating, or testing
Measurement system in a specific environment
Mechanical measurement system
C702S038000
Reexamination Certificate
active
06816794
ABSTRACT:
The present invention relates to an apparatus and method, notably to apparatus for inspecting products for contamination and to a method for operating such apparatus.
BACKGROUND TO THE INVENTION
Many products, notably foodstuffs, are inspected as they are produced or packaged to detect metallic impurities therein which might be harmful to the quality of the products and/or to a user of the product, notably if they were to be ingested. Its is therefore customary to pass such products through or past some form of metal detection device. Typically, such devices comprise two, three or more wire coils through one of which, the emitter coil, a pulsed or varying electric current is passed. This causes induction effects to be generated between the coils and an induced current to flow in the other, receptor, coil(s), which can be monitored using any suitable technique. Although, such devices usually operate with an emitter coil inducing a current flow in the other, receptor, coils, there have been proposals in which electric currents flow in each of the coils and it is the interaction of the induction effect, for example the change in phase and/or amplitude on the current flowing in one coil due to the effect of the other coil, which is monitored. Typically, the coils are generally planar circular loops of electric conductor located with the planes of the coils substantially parallel to one another upon a common axis. However, the coils may be of squared, triangular or other plan shape. If desired, ferrite rods or discs can be located within the coils or other means, for example a metal housing for the coils, can provided to shape the inductive field generated by the emitter coil and/or the object can be observed through an aperture in a metal or other screen so as to optimise the sensitivity of the receptor coil to changes caused by the presence of metals adjacent the device and to limit the area of the object scanned to reduce edge effects, for example to avoid scanning thinner edges of the object.
For convenience, the term metal detector will be used herein to denote any such device which monitors a change in the coupling effect between two coils, through at least one of which a pulsed or varying current is passed, in response to the proximity of a metal to the coils. Many forms of metal detectors are commercially available and used in detecting metal contamination of products.
If a metallic object passes adjacent the coils, the coils electrically couple with the object and the inductive effect of one coil on the other changes. Typically, the presence of a metallic object causes a change in the phase of the current induced in the receptor coil which can be observed. This effect is also noted where the metallic object is an electrolyte, for example the gravy or sauce in which solid food particles are carried. For convenience, the term metallic contamination of an object will be used herein to denote in general any electrolyte, metal or other material present in that object which causes a change in the signal produced by a metal detector when that object is located adjacent to the metal detector.
Typically, the object to be observed is passed generally parallel to the plane of the coils of the metal detector. However, if desired, the plane of the coils can be inclined to the line of travel of the object past the metal detector. Alternatively, the object can pass though the plane of the coils, usually axially through the loop of the coils. The term pass will be used hereinafter in respect to moving objects relative to the coils of a metal detector to denote passage through or parallel to the plane of the coils or at any angle intermediate these lines of passage.
In use, an operator passes a series of objects corresponding to the object to be observed past the metal detector. The passage of these objects will cause a series of references signals to be generated, whose characteristic amplitude, phase angle or other features can be determined, for example as a series of digital pulses or numbers defining the amplitude, phase and phase angle of the signal. Such characteristic, or reference signals can then be used to identify subsequent objects moved past the metal detector. The generation of the reference signals may also be carried out using a batch of samples of the actual objects to be observed and which are known to meet the metal contamination criteria for an acceptable product. In this case, slightly varying signals may be observed for each sample due to minor variations in the composition of the objects within each batch. The signals are averaged to produce the characteristic reference signal for the objects within each batch of samples.
The reference signal corresponding to an object is stored in a computer memory or other machine readable storage device so that it can be called up for comparison against the signal from another object of the same type passing the metal detector. Provided that the signal from the other object is, within acceptable limits, the same as the reference signal, the operator will know that the other object also meets the metal contamination requirements set for the calibration object. It is therefore customary to set up the signal stored in the memory to allow for an acceptable variance from the reference signal corresponding to manufacturing tolerances for the object to be observed. Such a signal incorporating such tolerances will be denoted hereinafter as the calibration signal for that product. As indicated above, it is also customary to carry out the calibration with a number of samples and to take the average of the signals from those samples to generate the calibration signal for that type of object.
It has been proposed that the computer controlling the storage and monitoring of the observed signals should carry out an averaging of the observed signals from a series of the same type of object so as to determine whether any optimisation of an initial calibration signal can be made having regard to the limits to acceptability laid down by the operator of the production line or process producing the objects to be observed. Such automated setting up and review of the calibration signal can be carried out at the initial start up of the production of the objects and/or can be carried out as an on-going process during the passage of the stream of objects past the detector.
However, the operator of the production line for the objects has little or no input in the control of the setting of the calibration signal or of the automatic setting up and optimisation of the calibration signal during the object observation process. Typically, the manufacturer of the metal detector will install the detector and will set up the initial limits within which the signal from the detector is to be treated as relating to an acceptable product on the basis of initial samples provided to him by the operator of the object production process and on the basis of tolerances for variation of the metal contamination permitted by the operator. These factors are incorporated into the software controlling the computer which carries out the automatic setting up and optimisation of the calibration signal. All of this requires expert operators and is time consuming.
In view of the complexity of the shape of signal which is generated by the metal detector, the area over which a signal is deemed to be acceptable is formulated as a box-like image and the limits of an acceptable signal are given in terms of the co-ordinates of the box and the general phase angle of that box to a datum line, for example the notional x axis of a display of the signal. The operator is provided with a two or three line display of alphanumeric symbols defining these features so that he can monitor the operation of the metal detector and verify that he has selected the correct calibration signal for use with a given object. However, once the limits of an acceptable signal have been set, the operator has little opportunity to vary the box within which an acceptable signal must lie, other than to switch between the
Hoff Marc S.
McAndrews Held & Malloy
Miller Craig Steven
Videojet Technologies Inc.
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