Method and apparatus for inspecting quality of manufactured articles

Abstract: There is disclosed a method for inspecting a physical feature on a surface of a manufactured article. First, a sensor (12) is provided adjacent to the article (1). Then, the surface (1a) of the article (1) is sensed by the sensor (12) while causing one of the sensor (12) and the article (1) to rotate about an axis perpendicular to the surfache (1a) of the article (1), to thereby obtain a signal which has peaks corresponding to the physical feature on the surface (1a) of the article. Subsequently the signal is processed and the processed signal is analyzed based on the number of the peaks, to thereby obtain information as to the physical feature on the surface (1a) of the article (1). An inspection apparatus suitable for practicing the above-mentioned method is also disclosed.

Description: BACKGROUND OF THE INVENTION Field of the Invention The present invention pertains to a method and apparatus for inspecting the physical feature of manufactured articles, and in particular the presence and number of attachments or the like attached to the articles. Prior Art Fig. 1 is a plan view showing a top end (manufactured article) of a usual aluminum can. The top end, designated at 1, includes a top-end body 2 having a sector-shaped opening portion 4 surrounded by a weakened seam 3 and a tab ring (attachment) 5 securely fixed to the top-end body 2 by caulking, and is provided with lip beads 6 and 6 so as to sandwich the opening portion 4 therebetween. When manufactured, the top end of the aforesaid construction is subjected to various inspections, which includes an inspection for the presence of the tab ring 5. The inspection of the tab ring 5 has hitherto been conducted by making the operators check each top end 1 visually or by obtaining images of the top surface of the top end 1 with an area sensing camera and inputting the image signals to an image processing device to process the images. However, the manufacturing number of top ends has increased rapidly due to a drastic increase in the demand for aluminum cans, and hence the operators tend to suffer from considerable burdens, thereby causing inspection errors easily. Furthermore, in the inspection using image processing techniques, it takes much time to carry out the image processing, resulting in low efficiency of inspection. In addition, it has been difficult to install an automated inspection system in a high-speed manufacturing line. US-A-4 140 072 describes a can lid forming apparatus including means for attaching a can opening key. A proximity field sensor is mounted in a doming die of the apparatus and generates a pulse logic signal as a can lid with a staked key is formed by the doming tool. A timing disc rotates in synchronism with each cycle of the tool and generates a pair of logic signals. A key monitor circuit is connected to respond to the signals to establish a latch, check latch and reset latch sequence for each cycle of the tooling. If the latch is not set, an appropriate output signal is generated indicating a key is missing from the lid. If the latch is not reset after being set, indicating a build-up of aluminum fines or the like on the probe, an appropriate signal is generated by a preconditioned probe monitoring circuit. The latter is connected to respond to the pulse logic signal and the reset signal to continuously check on the generation of the output pulse of the probe and produce a stop or alarm output if the logic pulse signal is not formed; indicating a sensor malfunction of the absence of the key. EP-A-0 304 164 describes an apparatus for inspecting the sealing surface of a container for defects. While the container is rotated, a beam of light is projected horizontally above and through a finish portion of said container. An optical detector detects the height of said sealing surface by detecting the location of a minimum in the light beam. Dips in the height indicate dips or saddles. Alternatively, an opaque bearing member is lowered onto the sealing surface in the path of the light beam to provide a reference indicative of the prevailing height of the sealing surface. Light passing between the underside of the bearing member and the sealing surface indicates a dip or saddle. SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a method for inspecting quality of manufactured articles by which the physical feature of a surface of an manufactured article can be positively and rapidly inspected with automation. Another object of the invention is to provide an inspection apparatus which can be utilized to carry out the aforesaid method. According to a first aspect of the invention, there is provided a method of inspecting a physical feature on a surface of a manufactured article, comprising the steps of: (a) providing sensing means adjacent to said article; (b) operating said sensing means to sense said surface of said article while causing one of said sensing means and said article to rotate about an axis perpendicular to said surface of said article, to thereby obtain a signal as to the attachment; and (c) subsequently processing and analyzing the signal, to thereby obtain information as to the attachment on said surface of said article; characterized in that said sensing means comprises a plurality of sensors disposed so as to sense points on said surface which are spaced by different distances from said axis perpendicular to said surface of said article; that said operating step (b) includes operating said plurality of sensors to produce the signal which has peaks corresponding to the attachment on the surface of said article; and that said processing step (c) includes obtaining information as to the position of the attachment on said surface of said article by comparing the positioning of the peaks of said signal with respect to each other. According to a second aspect of the invention, there is provided an apparatus adapted to inspect a physical feature on a surface of a manufactured article, comprising: holding means for holding said article; first sensing means disposed adjacent to said holding means for sensing said surface of said article; and rotating means for causing one of said first sensing means and said article to rotate about an axis perpendicular to said surface of said article; characterized in that said first sensing means comprises a plurality of sensors disposed so as to sense points on said surface which are spaced by different distances from said axis perpendicular to said surface of said article to thereby produce the first signal which has peaks corresponding to the attachment on the surface of said article; and that an information obtaining means is connected to said first sensing means for comparing the positioning of the peaks of said first signal with respect to each other to thereby obtain information as to the position of the attachment on said surface of said article. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a plan view of a top end of a usual aluminum can; Fig. 2 is a schematic plan view of an apparatus for inspecting quality of manufactured articles in accordance with the present invention; Fig. 3 is an enlarged view showing the position of a sensor; Fig. 4 is a block diagram of the inspection apparatus; Fig. 5 is a timing chart of the signals processed in the apparatus; Fig. 6 is a view similar to Fig. 2, but showing a modified apparatus in accordance with the present invention; Fig. 7 is a view similar to Fig. 3, but showing the apparatus of Fig. 6; Fig. 8 is a block diagram of the apparatus of Fig. 6; and Figs. 9 and 10 are timing charts for the apparatus of Fig. 6. DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION An apparatus for inspecting quality of manufactured articles in accordance with the present invention will first be described with reference to Figs. 2 to 4. In Fig. 2, the numeral 10 denotes a turret for holding top ends 1 for aluminum cans that are conveyed from a manufacturing line. The turret 10, which is in the form of a disc, is rotatable about an axis thereof, and is provided with a plurality of holding portions 11 formed on the periphery of an upper surface thereof in circumferentially equally spaced relation to one another. Each of the holding portions 11 has a circular shape of a diameter generally equal to the top end 1, and is rotatable about its axis. Thus, the top end 1 is securely received on the holding portion 11 by a vacuum, so that it can be rotated about an axis thereof by the rotation of the holding portion 11. In addition, a first sensor 12 for detecting the tab ring 5, which is, for example, comprised of an optical distance sensor (triangulation-type or quantity of reflected light-type), an ultrasonic sensor, an electrostatic sensor or an eddy-current sensor, is immovably disposed at a predetermined position above the periphery of the turret 10, and is operable to sense the distance between the sensor 12 and the top end 1 which is conveyed due to the rotation of the turret 10. As best shown in Fig. 3, the first sensor 12 is located above a prescribed holding portion 11 in such a manner that when a top end 1 without any defect is received by the holding portion 11 and rotated about its axis, the sensor 12 detects the tab ring 12 at least twice and the lip beads 6, and produces a first signal representative of the information as to the tab ring. Furthermore, a second sensor 13, which may be the one similar to the aforesaid sensor, is immovably located in a fixed position adjacent to the periphery of the turret 1 for detecting the top end 1 held by the holding portion or detecting the holding portion 11 itself, to produce a second signal representative of the cycle of rotation of the top end 1. In the preferred embodiment, a slit is formed in the holding portion 11, and the second sensor 13 is arranged so as to detect the slit to produce the aforesaid second signal. The aforesaid first sensor 12 is connected to a signal processing circuit or unit 20 which is operable to process the signal outputted from the first sensor 12 and convert it to a binary signal based on a prescribed threshold. This signal processing unit 20 and the second sensor 13 are further connected to a counting circuit or an analyzer 21 which is operable to analyze the binary signal transmitted from the signal processing unit 20 with reference to the second signal representative of the cycle of rotation, to produce data or an output signal from which the operator or machine can determine whether the top end 1 held by the holding portion 11 is of good quality or not. Moreover, a feed device 14 is disposed at a position symmetrical with respect to the axis of the turret 10 from the first sensor 12 and is operable to supply the holding portion 11, which has stopped at a position under the feed device 14, with a top end 1 which has been conveyed from the manufacturing line. Furthermore, an ejection device 15 is arranged adjacent to the feed device 14 for ejecting the top ends of good quality to a delivery line, while a discharge device 16 is disposed adjacent to the ejection device 15 for discharging defected top ends 1. The inspection method in accordance with the present invention will next be described. First, a top end 1, which has been conveyed from the manufacturing line, is moved to and held by a prescribed holding portion 11 of the turret 10 through the feed device 14 in such a manner that its top surface 1a to be inspected faces upwards. Thereafter, the turret 10 is caused to rotate through an angle equal to a central angle defined between two adjacent holding portions 11 with respect to the rotational center, so that the top end 1 is moved to the next position. The above-mentioned operation is repeated, and when the aforesaid top end 1 reaches a position where the first sensor 12 is arranged above it, the first and second sensors 12 and 13 are activated. Then, the first sensor 12 senses the top surface 1a of the top end 1 to produce a first signal which may have peaks produced by the presence of the tab ring 5 on the top surface 1a, and the signal processing circuit 20 processes the first signal to convert it into a binary signal, which is outputted to the analyzer 21. On the other hand, the second sensor 13 senses the rotation of the top end 1 to produce a second signal representative of the cycle of rotation of the top end 1 to input it to the analyzer 21, and in the analyzer 21, the first binary signal obtained for one cycle of rotation of the top end 1 is analyzed to produce data from which the information as to the presence of the tab ring 5 is obtained. More specifically, when the tab ring 5 is attached properly to the top surface 1a of the top end 1, the first sensor 12 produces a first signal which has peaks P as illustrated in Fig. 5. The number of the detected peaks P is three when the tab ring 5 is detected at the beginning of the sensing, but is two when a portion of the surface other than the tab ring 5 is detected at the beginning. This first signal is converted to a binary signal based on a prescribed threshold such that the peak P corresponds to "one" while the other portions correspond to "zero". The binary signal thus obtained is inputted to the analyzer 21, which analyses the signal to count the number of the peaks and judges the top end 1 as being of good quality when the number of the peaks is two or three. On the other hand, in the case where there is no tab ring 5 attached to the top end 1, the signal produced by the first sensor 12 has no peaks, and the analyzer 21 judges the top end 1 as being defective. In the foregoing, inasmuch as the top-end body 2 is provided with the lip beads 6 formed thereon, the signal produced by the first sensor 12 exhibits peaks lower than the aforesaid peaks P , but these lower peaks are removed during the conversion of the signal into the binary code. Any peaks caused by a foreign material adhering to the top end 1 may similarly be removed. After the analysis as to the presence of the tab ring 5 has been done as described above, the turret 10 is further rotated, and if defective, the top end 1 is discharged by the discharge device 16 while top ends 1 of good quality are ejected by the ejection device 16 to the delivery line. In this manner, the aforesaid operation is repeated to inspect all of the top ends 1 conveyed from the manufacturing line, and only the good top ends 1 are conveyed to the delivery line. In the aforesaid method, the top surface 1a of the top end 1 is inspected while rotating the top end 1. If the tab ring 5 is properly attached to the top surface 1a, the first sensor 12 transmits a signal with at least two peaks. Therefore, the presence of the tab ring 5 can be rapidly and reliably inspected by counting the number of the peaks. In addition, inasmuch as no image processing operation is required, a rapid inspection can be ensured, and hence the inspection operation for a high-speed manufacturing line can be easily automated. In the foregoing, although the top end 1 is caused to rotate about its axis during the inspection for the presence of the tab ring, the first sensor 12 may be constructed so as to rotate about an axis perpendicular to the top end 1. In addition, the inspection apparatus of the invention may be modified such that it can be used to inspect for the presence and number of irregularities on a disc-shaped article such as a badge, or to inspect any projections and recesses formed on the various manufactured articles. If a photo sensor is used as the first sensor 12, the presence and number of bright or dark portions on the articles may be inspected. Figs. 6 to 10 depict a modified inspection apparatus in accordance with the present invention in which a pair of first sensors 12a and 12b are immovably arranged at positions above the periphery of the turret 10 for detecting the tab ring 5 on the top end 1 which is conveyed by the rotation of the turret 10. As shown by the small circles 12a, 12b in Fig. 7, the aforesaid first sensors 12a and 12b are located on a straight line passing through a diameter of the top end 1 in such a manner that the distance of the sensor 12a from the central axis of top end 1 is shorter than that of the sensor 12b therefrom, and that, when a top end 1 without defects is rotated about the central axis thereof one time, the sensor 12a detects the tab ring 5 at least twice and the lip beads 6 while the sensor 12b detects only the lip beads 6. The first sensors 12a and 12b are connected to signal processing units 20a and 20b, respectively, which are further connected to the analyzer 21. The analyzer 21 includes three AND circuits 21a and 21c and a pulse count-digital comparator 21b and is operable to process the inputted signals. In the above embodiment, the turret 10 is rotated as is the case with the previous embodiment, and when the top end 1 is conveyed to a position below the first sensors 12a and 12b, the first sensors 12a and 12b and the second sensor 13 are activated. Then, the second sensor 13 senses the rotation of the top end 1 to produce a second signal (ROT signal) representative of the cycle of rotation of the top end 1 to input "one" to the analyzer 21 during one cycle of rotation of the top end 1, as illustrated in Fig. 9. In addition, the first sensors 12a and 12b sense the top surface 1a of the top end 1 to produce first signals which may have peaks produced by the presence of the tab ring 5 on the top surface 1a, and the signal processing units 20a and 20b process the first signals, respectively, to convert them into binary signals, which are outputted to the analyzer 21. More specifically, when the tab ring 5 is being attached properly to the top surface 1a of the top end 1, the first sensor 12a produces a first signal which has peaks P₁ based on the tab rings 5 and peaks P₂ based on the lip beads 6 while the second sensor 12b produces another first signal which has peaks P₃ caused by the lip beads 6, as illustrated in Fig. 9. The number of the detected peaks P₁ and P₂ of the signal produced by the first sensor 12a is four in total when a portion other than the tab ring 5 or the lip bead 6 is detected at the beginning of the sensing, and is six when the tab ring 5 or the lip beads 6 is detected at the beginning. On the other hand, the number of the detected peaks P₃ of the signal produced by another first sensor 12b is two when a portion other than the lip beads 6 is detected at the beginning of the sensing, and is three when the lip bead 6 is detected at the beginning. Furthermore, if the tab ring 5 is secured to a proper position between the lip beads 6, the sensor 12b detects the lip bead 6 at the same time when the sensor 12a detects the tab ring 5, so that the aforesaid peaks P₁ and P₃ are produced simultaneously. After first or second derivatives of the above first signals are obtained as necessary, the signals are converted into binary signals based on thresholds such that the peak P₁, P₂ or P₃ corresponds to "one" while the other portions correspond to "zero", and are transmitted to the analyzer 21. Then, in analyzer 21, a logical AND operation is carried out by the AND circuit 21a on the binary signals to produce an IN signal, which outputs "one" when the peak P₁ coincides with the peak P₃ and outputs "zero" when the peaks P₁ and P₃ do not coincide. When the IN signal has two or three portions indicating "one" during one cycle of rotation of the top end 1, the top end 1 is judged as being of good quality. Furthermore, the ROT signal inputted in the analyzer 21, is processed therein to produce a CK signal, which is active after the ROT signal becomes zero and remains unchanged for a prescribed period of time. The CK signal, however, becomes zero before the ROT signal becomes active next time. The pulse count-digital comparator 21b in the analyzer 21 begins to count the number of pulses of the IN signal when the ROT signal becomes "one", and works only when the ROT signal is active. When the ROT signal changes to "zero", the comparator 21b stops and holds the results at that time, and when the CK signal changes to "zero", it is reset and stops until the next ROT signal is produced. Thus, there is produced an output signal GO/NG, which outputs "zero" at the second peaks of the IN signal and outputs "one" at the fourth peaks, Then, a logical "AND" operation is carried out by the AND circuit 21c on the CK signal and the GO/NG signal, the result of which is "zero" when the top end 1 is judged as being "normal". On the other hand, if the tab ring 5 is shifted from its proper position, the signal produced by the sensor 12a has peaks P₁ due to the tab ring 5 and peaks P₂ due to the lip beads 6, while the signal produced by the sensor 12b has peaks P₃ caused by the lip beads 6, as illustrated in Fig. 10. However, the peak P₁ and the peak P₃ emerge at different times, and hence when the signal processing operation is carried out on the binary signals of the respective signals, the IN signal thus produced has no portion indicating "one" and is outputted entirely as "zero". In this case the top end 1 is judged as being "abnormal". Similarly, the signal processing operation is carried out on the ROT signal and the IN signal and further on the CK signal and GO/NG signal. This processed signal is outputted as "one" and the top end 1 is judged as being "abnormal". Furthermore, if no tab ring 5 is attached to the top-end body 2, the signal produced by the sensor 12a does not have peaks P₁. Accordingly, the IN signal produced by the AND operation on the binary signals, which are obtained similarly, has no portion that is outputted as "one", and is judged as being "abnormal". As described above, in the inspection method in accordance with the modified apparatus, if the tab ring 5 is attached to the proper position of the top end 1, the peak P₁ due to the tab ring 5 in the signal of the sensor 12a and the peak P₃ due to the lip beads 6 in the signal of the sensor 12b emerge at the same time. On the other hand, if the tab ring 6 is not in the proper position, the above peaks P₁ and P₂ are detected at different times. Accordingly, whether the tab ring 5 is attached to the proper position or not can be easily and surely inspected by judging whether time of detection of the peaks P₁ and P₃ coincides or not. In the foregoing, the sensor 12a is arranged so that it detects the tab ring 5 and the lip beads 6 while the sensor 12b is arranged so as to detect only the lip beads 6. However, both the sensors 12a and 12b may be located so as to detect both the tab ring 5 and the lip beads 6. Furthermore, more than two sensors may be provided under some circumstances.

Claims: A method of inspecting an attachment (5) on a surface (1a) of a manufactured article (1), comprising the steps of: (a) providing sensing means (12) adjacent to said article (1); (b) operating said sensing means (12) to sense said surface (1a) of said article (1) while causing one of said sensing means (12) and said article (1) to rotate about an axis perpendicular to said surface (1a) of said article (1), to thereby obtain a signal as to the attachment (5); and (c) subsequently processing and analyzing the signal, to thereby obtain information as to the attachment (5) on said surface (1a) of said article (1); characterized in that said sensing means (12) comprises a plurality of sensors (12a,12b) disposed so as to sense points on said surface (1a) which are spaced by different distances from said axis perpendicular to said surface (1a) of said article (1); that said operating step (b) includes operating said plurality of sensors (12a, 12b) to produce the signal which has peaks corresponding to the attachment (5) on the surface of said article (1a); and that said processing step (c) includes obtaining information as to the position of the attachment (5) on said surface (1a) of said article (1) by comparing the positioning of the peaks of said signal with respect to each other. An apparatus adapted to inspect an attachment (5) on a surface (1a) of a manufactured article (1), comprising: holding means (10, 11) for holding said article (1); first sensing means (12) disposed adjacent to said holding means (10, 11) for sensing said surface (1a) of said article (1); and rotating means (11) for causing one of said first sensing means (12) and said article (1) to rotate about an axis perpendicular to said surface (1a) of said article (1); characterized in that said first sensing means (12) comprises a plurality of sensors (12a, 12b) disposed so as to sense points on said surface (1a) which are spaced by different distances from said axis perpendicular to said surface (1a) of said article (1) to thereby produce the first signal which has peaks corresponding to the attachment (5) on the surface (1a) of said article (1); and that an information obtaining means is connected to said first sensing means (12) for comparing the positioning of the peaks of said first signal with respect to each other to thereby obtain information as to the position of the attachment (5) on said surface (1a) of said article (1). An inspecting apparatus as recited in claim 2, wherein said information obtaining means comprises a second sensing means (13) disposed adjacent to said holding means (10) for sensing the relative rotation of said article (1) to produce a second signal representative of cyclic period of relative rotation of said article (1), a signal processing unit (20a, 20b) operably connected to said first sensing means (12) for processing the first signal and an analyzer (21) operably connected to said signal processing unit (20a, 20b) and said second sensing means (13) for analyzing the peaks obtained during a predetermined cycle of relative rotation of said article (1). An inspecting apparatus as recited in claim 3, wherein said holding means comprises a turret (10) having said rotating means (11) which rotates said article (1). An inspecting apparatus as recited in claim 3, wherein said signal processing unit (20a, 20b) comprises a circuit for converting said first signal into a binary signal. An inspecting apparatus as recited in claim 3, wherein said analyzer (21) comprises a counting means for counting the number of peaks during one cycle of relative rotation of said article (1) to thereby obtain information as to the attachment (5) on said surface (1a) of said article (1).

Inventors: INOUE YOSHIHIRO C O SHOOHIN KA, ISHIZAKI HIROSHI C O FUJI OYAM, ITOH HAJIME C O SHOOHIN KAIHAT, ITOW ATSUO C O SHOOHIN KAIHATS, INOUE, YOSHIHIRO, ISHIZAKI, HIROSHI, ITOH, HAJIME, ITOW, ATSUO, INOUE, YOSHIHIRO, C/O SHOOHIN KAIHATSU CENTER, ISHIZAKI, HIROSHI, C/O FUJI OYAMA KOUJOU, ITOH, HAJIME, C/O SHOOHIN KAIHATSU CENTER, ITOW, ATSUO, C/O SHOOHIN KAIHATSU CENTER
Applicants: MITSUBISHI MATERIALS CORP, MITSUBISHI MATERIALS CORPORATION
Application year: 1990
Main classification: B07C5
IPC codes: B07C5