METHOD OF AND APPARATUS FOR TESTING OPTICAL SENSOR BASED CONTROL APPARATUS

Abstract: This invention relates to a method of and apparatus for testing optical sensor based control apparatus. An apparatus under test (18) includes sensors (11, 12) and (13). The received inputs are processed by hardware and software (16) and fed to a hardcopy output device (17). A linear electrical to optical converter (7) is driven by function generators (8) to feed a predetermined light pattern down an optical fibre (2, 2') to the sensors (11, 12 and 13). A controller (9) drives the function generators (8) to produce a predetermined light pattern which stimulates the apparatus under test (18) so that the hardcopy output device (17) produces a current performance characteristic of the apparatus which can be correlated with the predetermined light pattern. In this way, the apparatus can be tested without physical access to the apparatus hardware and software, and by suitable programming of the controller the predetermined light pattern can be directed to functionally test one or more portions of the apparatus.

Description: METHOD OF AND APPARATUS FOR TESTING OPTICAL SENSOR BASED CONTROL APPARATUS FIELD OF THE INVENTION This invention relates to a method of and apparatus for testing optical sensor based control apparatus, and in particular to the testing of quality control apparatus employing automated optical inspection or scanning of a web product. BACKGROUND TO INVENTION Flying spot laser scanners are considered essential tools in the production of continuous web materials such as photographic material. This is because such scanning is the only practical way of automatically inspecting the physical quality of 100% of the production volume. In this way, the flying spot scanner and associated detection apparatus can operate as quality control apparatus checking the web material output. Of course, it is important to have some means of checking that the laser scanner and the associated detection apparatus are correctly adjusted and performing to a known inspection standard. If in fact the inspection standard is too low, output quality is reduced and if it is too high, waste levels increase. Where the value of the web product is high, such inaccuracies can quickly adversely affect production costs. Accordingly, it is necessary to provide tight control of the scanner settings as well as the optical and electronic parameters of the detection apparatus. It is an object of the present invention to provide a method of testing such quality control apparatus which employ optical sensors to provide inspection or scanning of a product. SUMMARY OF INVENTION According to one aspect of the present invention there is provided a method of testing optical sensor based control apparatus, the method including the steps of:- feeding a predetermined light pattern into the optical sensor or sensor of said apparatus to stimulate the apparatus to function? monitoring the output of the apparatus; obtaining from the monitored output a current performance characteristic corresponding to the apparatus and correlated with said predetermined light pattern. In this way, it is possible to obtain a control performance characteristic for the apparatus. Thereafter, deviations from this characteristic can be ascertained. The advantages of this method are that there is total optical isolation of the detection part of the apparatus from the scanning part which is normally providing the light input into the optical sensors. Thus, there is no risk of the test method loading the apparatus electronics and disturbing the measurements. Also, manufacturers guarantees and service agreements for the apparatus should be unaffected. Furthermore, the present method is applicable to all maunfacturers models of apparatus. Therefore, it is apparent that the present method can be applied to apparatus employing multiple optical sensors to receive multiple scanner inputs. Only one set of test apparatus is in fact required. A significant advantage of the present invention is that the method exercises the apparatus itself without the addition of sensors, probes or test components to the apparatus. In a preferred embodiment of the invention, the method includes a step of selecting the predetermined light pattern to have one or more parameters directed to functionally test a portion only of the apparatus under test, and obtaining from the monitored output a current performance characteristic corresponding to that portion. In this way, the light pattern fed into the optical sensors can be arranged to fully exercise a particular receiver channel or a particular component thereof. Consequently, it is possible to obtain a full functional test of that channel and additionally provide quantative gain, frequency and other characteristic data consitituting an equipment signature. This is particularly important where the apparatus includes a large number of interrelated components. Hitherto, it has proved practically impossible, or alternatively very expensive, to attach appropriate test probes to isolated sections of the apparatus under test, The present invention does not require probes to be attached to specific sections of the apparatus but merely requires the feeding of a predetermined light pattern into the optical sensors. Conveniently, the method includes the step of correlating said monitored output with a stored performance characteristic of the apparatus. Thus, it is quite simple to compare the stored performance characteristic with the current performance characteristic to ascertain if there has been any fall off in performance. Preferably, the method includes the step of activating an alerting means in response to the current performance characteristic deviating a predetermined amount from the stored performance characteristic. Consequently, it is apparent that the present method can enable off line or on line condition monitoring of the apparatus under test. Conveniently, the current performance characteristic, and optionally the stored performance characteristic, can be produced as hard copy. It will be apparent that the method of the present invention is fully programmable so that an array of tests can be devised to test a series of specific functions of the apparatus under test. Consequently, it avoids the need for one instrument per function of the apparatus which quantative characterisation would normally require. Although the test method can be employed with a variety of optional sensor based apparatus, the method preferably is a testing quality control apparatus nethod, the apparatus under test employing automated optical inspection or scanning of a product. According to another aspect of the invention there is provided apparatus for testing optical sensor based control apparatus comprises a programmable signal generator, optical signal generating means arranged to produce an optical output in response to signals received from the programmable signal generator and means to couple with optical signals to an apparatus under test. BRIEF DESCRIPTION OF DRAWINGS An example of the present invention will now be described with reference to the accompanying drawings, in which:- Figure 1 illustrates a test system embodying the present invention attached to a quality control apparatus, Figure 2 illustrates a method of coupling a predetermined light signal to the apparatus under test, Figure 3 illustrates a test sequence which characterises the amplitude of frequency and response of a receiver channel under test. DETAILED DESCRIPTION OF AN EMBODIMENT OF THE INVENTION Referring to Figures 1 and 2, an optical sensor 1 comprises a portion of a quality control apparatus 18 receiving signals, in use, from a laser scanner. The sensor has attached thereto an optical fibre 2. having a fibre cladding 3 around a fibre core 4 as is known in the art. The optical fibre has a dimension of approximately 1mm diameter and is laid along the sensor window 5 of the sensor 1 with a triangular cross section etched glass piece 6 located at the end of the fibre. The etched glass piece reflects light from the optical fibre into the receiver window. The light reflecting surface is painted or shielded to prevent light reflecting off the web being mounted. It will be apparent that direct contact of the optical fibre with the sensor is not essential; however, light from the optical fibre should be directed entirely into the sensor windows. Referring specifically to Figure 1, the light for the optical fibre 2 is produced from a linear electrical to optical converter 7. The electrical signals actuating the converter 7 are provided by function generators 8 controlled by a controller 9 which can be commercially available devices. Additional function generators can be driven from a line 10 from the controller. In the example shown, the optical fibre 2 passes through controlled fibre optic relays 14 so that a plurality of optical fibres 2' can be attached to, in this case, three sensors 11, 12 and 13 of an apparatus under test. The modulated light flux from the fibres at 15 enters the respective sensor and is passed through the signal processing hardware and software 16 of the apparatus 18 to a hard copy output device 17. The controller 9 is programmed so as to drive the function generator 8 to modulate a laser diode or light emitting diode in the converter 7 which is coupled by optical fibre 2, 2' to the light sensors 11, 12 and 13 which comprise the sensors for the quality control apparatus 18 such as a web inspection system. The function generators are programmed to stimulate the sensors and apparatus electronics in such a way that the normal display equipment of the apparatus under test records data which quantitively characterise the apparatus under test. The laser diode or light emitting diode in the converter 7 should be capable of fast intensity modulation. In some cases the detector part of an optical based inspection system will require testing at much higher rates than those at which its own light source can be modulated. Figure 3 illustrates an example of the results that can be obtained with the method embodying the present invention. The specific nature of the programming of the function generators 8 will be apparent to a person skilled in the art and are dependent in many respects on the apparatus which is being tested. Figure 3 illustrates an example of the hard copy output from the apparatus being tested in Figure 1. It can be seen that the test signal incorporates a frequency marker and amplitude marker as references and the test signal comprises a sine wave, amplitude modulated by a ramp with the sine wave frequency automatically increased in logarithmic steps. Consequently, it can be seen that by appropriate programming of the controller 9, the apparatus 18 under test can be stimulated to function and to produce a current performance characteristic correlated to the light pattern produced by the controller. It will be apparent to a person skilled in the art that the light pattern provided down the optical fibre 2 can be altered so as to test a particular channel of the apparatus 18 or particular portions of the processing hardware. Thus, there is no necessity to physically access the circuitry in the hardware processing section so that there is no risk of disturbing the apparatus electronics. This means that the manufacturers guarantees and service agreements should be unaffected. It will be apparent that the apparatus shown in Figure 1 can be operated as an off line or an on line condition monitoring arrangement. It will also be apparent to a person skilled in the art that the output of the system under test can be compared with earlier tests to see whether there has been any deviation in the apparatus performance. It is believed to be an inventive concept to convey optical test signals via fibre optics to sensor inputs of an apparatus and to devise test signals fed to those sensors which use the exisiting apparatus own. output devices as quantitative monitors of the apparatus functions.

Claims: CLAIMS 1. A method of testing optical sensor based control apparatus, the method including the steps of :- feeding a predetermined light pattern into the optical sensor or sensors of said control apparatus to stimulate the apparatus to function; monitoring the output of the apparatus; obtaining from the monitored output a current performance characteristic corresponding to the appratus and correlated with said predetermined light pattern. 2. A method according to Claim 1 including the step of selecting the predetermined light pattern to have one or more parameters directed to functionally test a portion only of the quality control appratus under test and obtaining from the monitored output a current performance characteristic corresponding to that portion. 3. A method according to Claim 1 or Claim 2 including the step of correlating said monitored output with a stored performance characteristic of the apparatus, 4. A method according to any preceding claim including the step of producing a hard copy of the current performance characteristic. 5. A method according to Claim 3 including the step of producing a hard copy of the current and stored performance characteristics. 6. A method according to claim 3 or Claim 5 including the step of activating an alerting means in response to the current performance characteristic deviating a predetermined amount from the stored performance characteristic. 7. A method according to any preceeding claim being a testing quality control apparatus method, which apparatus employs automated optical inspection or scanning of a product. 8. Apparatus for testing optical sensor based control apparatus comprises a programmable signal generator, optical signal generating means arranged to produce an optical output in response to signals received from the programmable signal generator and means to couple with optical signals to an apparatus under test. 9. Apparatus according to Claim 8, wherein said programmable signal generator comprises a function generator driven by a controller and said optical signal generating means comprises a linear electrical to optical converter. 10. Apparatus according to Claim 8 or Claim 9, wherein said coupling means comprises an optical fibre or fibres, the optical signal generating means being arranged to feed a predetermined light pattern to said fibre or fibres.

Inventors: DAVIS PAUL MICHAEL, DAVIS, PAUL, MICHAEL
Applicants: EASTMAN KODAK CO, KODAK LTD, EASTMAN KODAK COMPANY, KODAK LIMITED
Application year: 1989
Main classification: G01M11
IPC codes: G01M11, G01R31