GB2271846A - Inspecting parts. - Google Patents

Abstract

An apparatus for inspecting parts conveyed to an image pick-up device inspecting means (A) by a supplying and arranging means (B) and a conveying means (1b), and an image processing unit (1j) being provided for classifying the parts as acceptable parts and unacceptable parts, the acceptable parts being ejected by means of an air nozzle on the basis of the inspection result. Embodiments having a one-sided hanging chute (fig 3), a V-shaped chute (fig 12) and an inclined chute (not shown) for delivering the part for inspection are described. <IMAGE>

Description

A METHOD OF AND APPARATUS FOR INSPECTING PARTS The present invention relates to apparatus for inspecting step-shaped and plateshaped parts and to a method which inspects step-shaped parts, such as screws, rivets and the like, and plate-shaped parts (including block-shaped parts) for their external appearance and shape, colour, and symbols such as stamped letters, and which automatically removes foreign parts or defective parts with wrong size, wrong shape, wrong plating, wrong letters, or the like which may have been mixed with the correct parts in a manufacturing process, a conveying step between manufacturing processes, or a packing or transportion step or the like.

When inspecting step-shaped parts such as screws and the like, it has been proposed in Japanese First Publication Tokkaisho 62-49203 (Figures 21 and 22), to supply the screws to a stepped roll conveyor 6b by means of a parts feeder 6a and to sort the screws by determining their head diameter. Only one kind of screws 2 with the same head diameter are hung in a hanging posture by a tapered roll conveyor 6c, supplied to an inspection unit D by means of a hanging conveyor belt 6d, and inspected for the screw shape by means of a one-dimensional image sensor 6f which operates a sorter 6a.

When inspecting various plate-shaped parts, as shown in Figure 35 (Figure 36 is a cross-sectional view taken along line R' - R' in Figure 35 and Figure 37 is a fragmentary view taken in the direction of arrow Q in Figure 36), the parts 3 are carried onto an inclined track 122 by means of a parts feeder 121 and their external dimensions are inspected by means of a one-dimensional line sensor 123 mounted on the inclined track 122, acceptable parts being put in an acceptables bin 125 and unacceptable parts being put in an unacceptables bin 126 by means of a rotary actuator 124.In this case, a separator gate 127 (Fig. 38) is formed on this side of the one-dimensional line sensor 123 on the inclined track 122 and thanks to the separator gate 127 the plate-shaped parts 13 being conveyed are separately supplied to the one-dimensional line sensor 123 (Figure 37) one after another so that they may not adjoin each other.

However, the prior parts inspecting apparatus and methods have the following problems.

In case of step-shaped parts such as screws or the like.

(1) Since the parts are carried and supplied for inspection in a hanging state, the hanging conveyor belt 6d, the stepped roll conveyor 6b and the tapered roll conveyor 6c need to be replaced and adjusted so as to fit the diameter of parts to be inspected.

(2) The inspecting apparatus is often stopped because the parts are clogged up at the point of transfer between the tip of the tapered roll conveyor 6c and the hanging conveyor belt 6d shown in Figure 21.

(3) Since the arrangement and separation of parts and their selection based on their head diameter are performed mechanically, the inspecting apparatus is large and complicated.

(4) Since the parts are carried and supplied for inspection by means of the hanger conveyor belt 6d disposed on both sides of the neck of the parts, the screw part hidden by the hanger conveyor belt 6d (shown in Figure 22) cannot be inspected. Small-sized screws in particular cannot be inspected since their hidden part is. relatively large.

(5) In case of inspection by means of the one-dimensional line sensor 6f, an acceptable part may be erroneously judged as unacceptable if the parts are conveyed to the line sensor 6f contiguously to each other because of fluctuations of the conveying speed caused by vibration during conveyance or by slip between the parts and the belt.

(6) A head shape such as hexagonal, square, or the like and a driver-slot shape of the screw head, of plus type or minus type cannot be inspected.

On the other hand, in case of inspection of plate-shaped parts.

(7) Since a one-dimensional line sensor 123 is used, a separator needs to be provided on the way to the sensor or inspecting part. However, since it is difficult to design a shape of separator gate which can separate even various plate-shaped parts without clogging, the inspecting apparatus is often stopped by clogging of parts at the separating part.

(8) The speed of a plate-shaped part passing the one-dimensional line sensor 123 fluctuates because of vibration during conveyance or slip of the parts, so that misjudgements may be made.

(9) If a specified posture of the plate-shaped parts is not kept when they pass the onedimensional line sensor 123, the shape inspection cannot be made.

(10) Since the one-dimensional line sensor 123 is used, the colour of and letters on the plate-shaped parts cannot be inspected.

(11) A shape, colour and letter in the peripheral surface of the plate-shaped parts cannot be inspected.

(12) Since acceptable and unacceptable parts are sorted and ejected through a sorting and ejecting mechanism disposed at the end of the inclined track, the acceptable parts and unacceptable ones are ejected in the same direction as the conveying direction and unacceptable parts can be mixed in acceptable ones by failure of the sorting and ejecting mechanism or by change of the dropping direction when dropping an unacceptable part.

It is an object of the invention to provide a parts inspecting apparatus which has a high inspection accuracy and processing performance and is simple and compact in structure, and also to provide an inspecting method using the apparatus.

The present invention is apparatus for inspecting step-shaped parts comprising means for supplying and arranging parts, means for conveying parts, means for inspecting parts, image processing means, and means for ejecting parts, wherein: the means for supplying and arranging parts has a one-side hanger guide widening toward its downstream end, the means for conveying parts has a one-side hanger chute conveying the parts placed in a one-side hanging posture by the one-side hanger guide, the means for inspecting part has at least one image pickup device out of an image pickup device taking an image of either the plan view or the side view of the parts to be inspected, the image processing means has an image processing unit which is connected with the image pickup device and inspects and determines the shape and the like of parts to be inspected by processing and analysing an image of them, and the means for ejecting parts has an ejecting unit which ejects the parts as acceptable parts and unacceptable ones on the basis of signals generated by the image processing unit.

The present invention is also apparatus for inspecting parts comprising means for supplying parts, a means for arranging and conveying parts, means for inspecting parts, image processing means, and means for ejecting parts, wherein: the means for supplying parts has a unit controlling a quantity of parts to be supplied for inspection, the means for arranging and conveying parts has a V-grooved chute whose slants forming the V-groove becomes gradually lower in height toward its downstream end, the means for inspecting parts has at least one image pickup device out of an image pickup device taking an image of either the plan or side view of the parts to be inspected, the image processing means has an image processing unit which is connected with the image pickup device and inspects and determines the shape and the like of parts to be inspected by processing and analysing an image of them, and the means for ejecting parts has an ejecting unit which ejects the parts as acceptable parts and unacceptable ones determined by the image processing unit.

The present invention is further a method of inspecting step-shaped parts comprising: (A) placing parts to be inspected in a one-side hanging posture, (B) conveying the parts to be inspected in a one-side hanging posture having a specified inclination, (C) taking images of the parts in the course of conveyance by means of an image pickup device, (D) processing and analysing the images and determining the parts to be acceptable or unacceptable, and (E) ejecting the parts as acceptable parts and unacceptable ones.

The present invention is additionally a method of inspecting parts comprising (a) controlling the quantity of parts to be inspected, (b) arranging and conveying the parts to be inspected, (c) taking images of the parts to be inspected in the course of conveyance by means of an image pickup device, (d) processing and analysing the images and determining the parts to be acceptable or unacceptable, and (e) ejecting the parts as acceptable parts and unacceptable ones.

Since the supply and conveying of parts to be inspected can be performed without being based on their external dimensions, the parts to be inspected are not clogged in the course of supplying and conveying them and can be supplied and conveyed to the inspecting unit in a stable state even if foreign parts are mixed in them. Furthermore it is not necessary to replace or adjust any parts of the apparatus even if specifications of parts to be inspected are changed. Therefore, the apparatus can be simplified and operated without operator for a long time. Also, since a transparent member is used in the inspecting part, an image of the whole part to be inspected can be taken and the reliability of inspection of parts is also improved.Moreover, even when adjoining plate-shaped parts are in contact with each other, the apparatus can recognise and determine the external shape and dimensions of each whole plate-shaped part. By blowing parts determined as acceptable ones of the inclined track in a direction nearly perpendicular to it with air in the acceptables ejecting part, the apparatus can separately eject the acceptables without mixing unacceptable parts with acceptable ones even if the air pressure is insufficient or shut off due to failure of an electromagnetic valve. As described above, the invention can implement a parts inspecting apparatus which can accurately judge the shape and dimensions of each whole part to be inspected, can be operated without an operator for a long time without clogging of parts to be inspected, and furthermore is small.

Embodiments of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a plan view of a screw inspecting apparatus, according to the present invention, of the one-side hanger chute type; Figure 2 is a front elevation of the apparatus of Figure 2; Figure 3 is a detailed view of part A, which is an inspecting means of Figure 1; Figure 4 is a detailed view of the means which arranges parts in a one-side hanging state of a parts feeder la of the invention; Figure 5 is a fragmentary view taken in the direction of the arrows G-G in Figure 4; Figure 6 is a cross-sectional view on line V-V in Figure 4; Figure 7 is a detailed view of a one-side hanger chute lb used in Figure 1; Figure 8 is a cross-sectional view on line J-J in Figure 7; which is an explanatory drawing of the inspecting part; Figure 9 is a cross-sectional view on line K-K in Figure 7, which is an explanatory drawing of the ejecting part; Figure 10 shows inspection features of a screw; Figures 11A to l lJ are explanatory drawings of processing steps in an image processing unit of the invention; Figure 12 is a plan view of a screw inspecting apparatus of V-grooved chute type according to the invention; Figure 13 is a front view of the apparatus of Figure 12; Figure 14 is an enlarged cross-sectional view on line R-R in Figure 12; Figure 15 is a detailed plan view of the V-grooved chute of Figure 12; Figure 16 is a detailed front view of the V-grooved chute; Figure 17 is a view in the direction of the arrows S-S in Figure 16;; Figure 18 is a cross-sectional view on line T-T in Figure 16 and is an explanatory drawing of the V-groove; Figure 19 is a detailed plan view of the inspecting part C and the V-grooved inspecting chute 3b; Figure 20 is a cross-sectional view on line U-U in Figure 19; Figure 21 is an explanatory drawing of an existing screw inspecting apparatus; Figure 22 is an enlarged view of a belt conveyor part D in Figure 21; Figure 23 is a plan view of a washer inspecting apparatus according to the invention; Figure 24 is a cross-sectional view on line J'-J' in Figure 23 and is an explanatory drawing of an inspecting part; Figure 25 is a view in the direction of the arrow P in Figure 24; Figure 26 is a cross-sectional view on line E-E in Figure 23, and is an explanatory drawing of an inclined track; Figure 27 is a cross-sectional view of an inspecting part of a further embodiment;; Figure 28 is a cross-sectional view on line K'-K' in Figure 23 and is an explanatory drawing of an ejecting part; Figure 29 shows inspection features of a washer; Figures 30 and 31 are a flowchart of a process based on inspection of a plan view of washers in an image processing unit of the invention; Figures 32A to 32J are explanatory drawings of the process of Figures 30 and 31; Figure 33 is a flowchart of image processing of a side view of the washers in the image processing unit of the invention; Figures 34A, 34B and 34C are explanatory drawings of the process of Figure 33; Figure 35 is an explanatory drawing of an existing washer inspecting apparatus; Figure 36 is a cross-sectional view on line R'-R' in Figure 35 and is an explanatory drawing of the inspecting part D';; Figure 37 is a view in the direction of the arrow Q in Figure 36 and is an explanatory drawing of the inspecting part D'; and Figure 38 is an explanatory drawing of a separating gate of the feeder in a washer inspecting apparatus according to the prior art.

In a first embodiment the parts to be inspected are step-shaped in particular screws, and subsequent references herein to screws should be understood to encompass other stepshaped parts. Figures 1 and 2 are respectively a plan view and a front elevation showing overall a screw inspecting apparatus using a one-side hanger chute for feeding screws, and Figure 3 is a detailed cross-sectional view on line J-J in Figure 1 of its inspecting means A.

Screws 2 put in a parts feeder la are arranged in a posture of single-side hanging in the parts feeder and supplied to a one-side hanger chute lb on a linear feeder lg. The part of the one-side hanger chute directly holding the screws in the inspecting means A is made of transparent material such as tempered glass or the like and in the course of conveying the screws through the inspecting means A a CCD camera 1c takes in an image of an external side view of a screw 2 and then an image processing unit lh analyses and recognizes the image to judge the external shape and dimensions in side view of the screw 2.

By having a CCD camera ld disposed also just above the screw heads, the inspecting means can inspect the shape of the screw-driver slot of the screw heads which is of plus or minus type and can also automatically eject a defective or foreign screw.

Both of the CCD cameras ic and ld are connected with the single image processing unit lh (the electrical connections are not shown in the Figure).

Figure 4, which is an enlarged detailed view of part B in Figure 1, shows a means for arranging screws in the parts feeder la in a one-side hanging posture. Figure 5 is a fragmentary view taken in the direction of the arrows G-G in Figure 4 and Figure 6 is a cross-sectional view on line H-H of Figure 4.

Each of the screws flows into part B with its head leading (2b) or trailing (2a).

In this case, by widening a one-side hanger guide lk toward its end downstream in the direction of conveyance, all the screws supplied to part B can take a posture of one-side hanging regardless of diameters, type and the like and screws other than acceptable ones can also be supplied to the inspecting means A.

In this manner, this feeding and arranging means can be used to feed and arrange many kinds of screws since it can make screws varying in dimensions or types adapt a oneside hanging posture by means of the one-side hanger guide lk in the parts feeder la. This feeding and arranging means does not clog the screws in the course of conveyance since the one-side hanger guide lk can arrange and convey them independently of their orientation with respect to the direction of conveyance.

Figure 7 is a detailed view of the one-side hanger chute lb viewed from the CCD camera looking in the direction of P in Figure 1, and in Figure 7 the screws to be inspected are conveyed from right to left. A cross-sectional view on line J-J in Figure 7 of the inspecting means A taking images of the external shape of the screws is shown in Figure 8 and a cross-sectional view of the means for ejecting the screws determined to be acceptable (cross-sectioned on line K-K in Figure 7) is shown in Figure 9.

The single-side hanger chute lb, which is a conveying part of the inspecting apparatus, is arranged as follows so that the screws may be inspected as they are being conveyed.

The one-side hanger chute lb conveys screws inclined at 50 degrees to the ejection point lm and keeps them in the same posture even after inspection made during conveyance. The one-side hanger chute lb has a base In whose part 1q opposite to the inspecting means A has been made into an opening with a member of tempered glass, so that the CCD camera lc may take an image of the screws 2 by transmitting light from a two-dimensional light emitting illuminator le through the opening 1q. In the inspecting means A, the CCD camera 1 c which is disposed perpendicularly to the longitudinal direction of the screw 2 and the two-dimensional light emitting illuminator le are disposed facing each other with the screw 2 between them.And by disposing another camera ld in the longitudinal direction of the screw 2 and just above its screw head, the slot shape of the screw head can be discriminated between plus type and minus type. Furthermore, by using a color CCD camera as the CCD camera ld to be disposed just above the screw head, the screw color also can be discriminated. The embodiment makes an inspection by using two CCD cameras, but the inspection can be also made by using one or three or more CCD cameras in response to the inspection items.

Still furthermore, if the whole one-side hanger chute lb is made of tempered glass, joints in the inspection means A can be removed and troubles in conveyance such as clogging of screws or the like in the joints can be obviated or mitigated.

In the embodiment described above, the screws are inclined at fifty degrees, but this angle can be set at any angle according to parts to be inspected.

The ejecting unit will now be described with reference to Figure 9. The ejecting unit, which is composed of an air nozzle If connected to an air supply and an acceptables chute lr, blows off only acceptable screws from the screws inspected by the image processing unit lh in the inspecting means A by means of the air nozzle 1 f to eject them into an acceptables box lj (Figure 1).In this case, by suitably controlling the time from when a screw is judged to be a defective or foreign one by the image processing unit to when the air of the air nozzle if is stopped so that the screw is conveyed from the inspecting part to the acceptables ejecting part in this time, then the screw judged to be a defective or foreign one is conveyed to the unacceptables ejecting chute li at the end by the one-side hanger chute lb without being blown off at the ejecting unit and is instead ejected into the unacceptables box is (Refer to Figure 1). However, to control the air nozzle if so as to identity and eject the screw judged to be a defective or foreign one, it is necessary to control exactly the setting of the apparatus.Hereupon, by setting the time when the air nozzle is off at the same period as when several screws before and behind the defective or foreign screw are passing through the acceptables ejecting unit, the possibility that the defective or foreign screw may be mixed in acceptable screws can be easily removed. As a result, the unacceptables box comes to contain not only acceptable screws but also unacceptable ones, but this does not create a problem as compared with the trouble caused when unacceptable screws are mixed in with acceptable ones, since the number of unacceptable screws is far less than the number of the inspected screws.

In an existing apparatus, for example, using as the ejecting method the blowing off of a defective or foreign screw could result in unacceptable screws being mixed in with acceptable ones when a screw judged to be a defective or foreign one is not blown off due to a failure in the air supply or an air valve. The invention can obviate or mitigate the problem of defective or foreign screws being mixed in with acceptable ones because of an external cause as a mechanical trouble or the like, since the invention has adopted a method of blowing off unacceptable screws with air to eject them, as described above.

Next, an inspection method used in the image processing unit lh is described as follows:1. A camera with a shutter has been used as the CCD camera so as to take in a static image even during vibration or one-side hanging conveyance.

2. The image processing unit generates in itself timing signals for taking images with the CCD camera and progresses consecutively and repeatedly through the steps of image taking, processing and inspecting by issuing a trigger signal for taking in the next image immediately after having taken in, analyzed and recognized the previous image (this method is called an internal trigger method).

3. Even if an image taken in contains plural images of screws, the shape of each of the screws can be judged.

Figure 10 is a drawing showing inspection features of a screw, and the image processing unit inspects the total length L1, screw length L2, head height L3, head diameter W1, screw diameter W2, head shape M, thread pitch W3 and driver-slot shape N of a screw.

Figures 11A to l 1J are model drawings showing a method of shape recognition and judgement of screws inside the image processing unit in the embodiment. A part of the inspection processing method is described in the following.

(1) Method of processing the shape and dimensions of a screw.

1 : A raw image is taken in from the CCD camera and is converted into a 2-level image by a threshold value for making a black and white 2-level image (Figure l l ).

2 : Expansion and contraction are made by means of morphology (Figure 1 lib).

3 : Logical operation (exclusive-OR) is made between the images 2 and 1 (Figure lic).

4 : Points a and b are detected and measured on a line 1 set in advance in the screen, and the distance between the points a and b is determined as the screw diameter (Figure liD).

5 : Points c and d are detected and measured on the line 2 which passes through the middle point of the segment a-b and is in parallel with the Y-axis, and the distance c to d is determined as the total length of the screw (Figure liE).

6 : Point e is detected on a line 3 set in advance in the screen by measuring upward from the intersection point x of the lines 3 and 2, and point fis detected on the line 3 by measuring downward from the point x (Figure 1 iF). Usually the distance between the points e and f is determined as the head diameter.

Now then, if screws are in contact with each other (Figure 1 lug), since the distance between points x and f for the upper screw is longer than the distance between the lines 2 and 2', the two screws are judged to be in contact with each other, and the distance x to fis replaced with x to e and the distance (x to e) + (x to e) is determined as the head diameter.

In the same manner, in case of the lower screw, the distance (x' to f) + (x' to f) is determined as the head diameter. In case that consecutive three or more screws are in contact with each other at both sides of each head, the distance between the middle points M of the respective screws is determined as the head diameter.

7 : A point measured toward the left from a point of intersection of the line 3 and the line 4 which passes through the middle point between the points a and e and is perpendicular to the line 3 is set as point g, and another point measured toward the right from it is set as point h. The difference between the distance g to h and the distance c to d is determined as the screw length (Figure 11H).

8 : Points i and j are detected and measured on the line 5 set in advance in the screen, and the inclination of the screw is obtained from the middle points of the segments a-b and ij to compensate the respective data (Figure 11I).

9 : A number is given to each feature in the image in Figure 11C (referred to as labelling), and a screw pitch is found for the respective screw threads between the lines 1 and 5.

(2) Method of processing the shape (type) of a screw head 1 : A raw image is taken in from the CCD camera and is converted into a 2level image by a threshold value for making a black and white 2-level image (Figure l lA).

2 : Points a and b are detected and measured on the line 1 (Figure 11D).

3 : Points c and d are detected and measured on the line 2 which passes through the middle point of the segment a-b and is in parallel with the Y-axis, and the distance c to d is determined as the total length of the screw (Figure 11E).

4 : Point e is detected on the line 3 set in advance in the screen by measuring upward from the point of intersection x of the lines 3 and 2, and point f is detected on the line 3 by measuring downward from the point x (Figure 1 iF).

Now then, if screws are in contact with each other (Figure l lG), since the distance between points x and f for the upper screw is longer than the distance between the lines 2 and 2', the two screws are judged to be in contact with each other, so the screw image is divided into two by the middle point M between the lines 2 and 2' and then the following process is made.

5 : Label is made and the vertical and horizontal end positions (called a fillet radius) of the objects are found.

6 : Points i and j are detected and measured on the line 5, the inclination of the screw is found from the points a and i, a mask image prepared in advance of an acceptable screw is rotated according to the obtained centre of gravity and inclination, and a logical comparison operation is made between the images.

7 : A mask having the found fillet radius is put over the image, and the head shape is judged from the area inside the mask.

If the parts to be inspected are rivets, a line 6 set in advance in the screen is detected and then the head shape is judged from a difference in length between the lines 3 and 6 (Figure 11J).

(3) Method of determining a driver-slot shape such as plus type, minus type or the like 1: An image is taken.

2 : The image is filtered to emphasise edges of the image.

3 : A mask is put over the image and then judgement is made from the sum total of brightness inside the mask.

(4) Method of determining whether plating is made or not.

1 : A full-colour image is taken in by means of a colour camera.

2 : The image is separated by hue, chroma and value of colour, and whether plating is made or not is judged from the found respective values.

Since inspection is made in this manner, if the conveying speed is so fast as to exceed the processing speed of the image processing unit, screws not inspected are conveyed to the end as they are and many screws not inspected come to be ejected at the unacceptables ejecting side. To mitigate this problem, it is sufficient to detect an excessive speed by measuring the conveying speed of screws by means of an optical fibre sensor tt (refer to Figure 9) and the like and control the conveying speed of the screws.

By now, an inspecting apparatus and inspecting method for screws have been described, but these can be also applied to other step-shaped parts such as rivets and the like.

Next, an apparatus and method for inspecting parts which cannot be hung down by a one-side hanger are described in a second embodiment of the invention.

Figures 12 and 13 are respectively a plan view and a front elevation showing the whole screw inspecting apparatus using a V-grooved chute method according to the second embodiment of the invention. Figure 14 is an enlarged cross-sectional view on line R-R of the inspecting means c in Figure 12.

Screws 4 put in a parts feeder 3e are supplied to a V-grooved chute 3a, are arranged in a line on the V-grooved chute, and the screws are conveyed in the attitudes 4a and 4b (refer to Figure 16).

The screws 4 arranged in this manner are supplied to a V-grooved inspecting chute 3b as they are arranged. As the slopes of the V-grooved chute 3a and the V-grooved inspecting chute 3b are different, the speed of the screws changes when the screws are transferred onto the V-grooved inspecting chute, and even if the screws were being conveyed in contact with each other, when they are transferred onto the V-grooved inspecting chute a gap is made between the screws, so the screws are conveyed out of contact with each other on the V-grooved inspecting chute.

A part of the V-grooved inspecting chute facing the inspecting part C is made of transparent material such as glass or the like. A CCD camera Ic catches from a side the screw 4 being conveyed through the transparent part and takes in an image of the external shape of the screw 4. The image processing unit lh analyses the image, judges the external shape, dimensions and colours of the screw from its side, and distinguishes acceptable screws from defective or foreign screws on the basis of the result and automatically ejects them. The above-mentioned matter is an outline of the second embodiment.

Figures 15 and 16 are respectively a detailed plan view and front elevation of the V-grooved chute 3a supplying and arranging screws. A method using this chute has the feature that it does not arrange screws in the parts feeder 3e as in the one-side hanger chute method but rather it arranges the screws 4 on the V-grooved chute 3a only by supplying them to the V-grooved chute 3a in amounts controlled by the parts feeder 3e and a gate which are a parts supplying unit.

Thus, the groove chute 3a on the linear feeder lg plays the role of receiving supplied screws 4, arranging them, and transferring them to the next V-grooved inspecting chute 3b.

Figure 17 is a view in the direction of the arrows S-S in Figure 16 and Figure 18 is a cross-sectional view on line T-T in Figure 16.

In the V-grooved chute 3a, the surfaces forming the V-groove are made high enough initially to receive many screws (refer to Figure 17), and are made gradually lower and lower, as shown in part B in Figure 15, as screws are being conveyed downstream, and are made low enough in the part to deliver the screws to the V-grooves inspecting part 3b, as shown in Figure 18. To form the V-grooved chute 3a in such a manner as this makes it possible to arrange in a line also short-body screws, cylindrical parts and the like which cannot be conveyed by a one-side hanger chute. In such a manner as this, screws of various types and sizes arranged by the V-grooved chute 3a can be conveyed to the inspecting part C, even if they are in contact with the upper edges x and y of the V-groove as shown in Figure 18.

If necessary, as shown in Figure 12, the apparatus can also be arranged so as to return the uninspected screws 5 which have been blown off and dropped outside the V-grooved chute to a supplying unit such as the parts feeder 3e or a hopper and the like by means of a belt conveyor 3d or the like.

Figures 19 and 20 are, respectively, enlarged plan and front views of the V-grooved inspection chute 3b including the inspecting part C, which explain the V-grooved inspecting chute 3b.

The screw 4 conveyed on the V-grooved inspection chute is inspected when it passes through the inspecting position of the inspecting part C in which a CCD camera 1c and a two-dimensional light-emitting illuminator le are set, and after the inspection it is conveyed to the ejecting position lm (refer to Figure 12) in the same posture. In the inspecting position, the CCD camera 1c is disposed perpendicularly to the inspection chute, and the two-dimensional light-emitting illuminator le is disposed so as to face the CCD camera 1c with the screw 4 between them. At least the inspecting part C of the Vgrooved inspection chute is made of a transparent member (3c) such as tempered glass or the like.The CCD camera 1c takes an image of the screw 4 with light being transmitted through the transparent member from the two-dimensional light-emitting illuminator le, and the image processing unit lh inspects and tests for the shape, colour and the like of the screw. The inspecting method in the image processing unit lh is the same as that in the first embodiment.

A method of blowing off and ejecting acceptable screws in the same manner as the first embodiment has been adopted as an electing method, which prevents defective or foreign screws being mixed in with acceptable screws because of an external cause such as a mechanical trouble and the like. Thus, as shown in Figure 12, a method is adopted in which only acceptable screws out of the screws inspected in the inspecting part C by the image processing unit lh are blown off to the acceptables chute lr by the air nozzle if and ejected to the acceptables box lj.

Apparatus as described in the second embodiment above using the V-grooved chute can be applied not only to step-shaped parts but also to cylinder-shaped parts to be inspected.

Next, another embodiment will be described in which the parts to be inspected are plate-shaped parts, in particular an internally-toothed lock washer.

Figure 23 is a plan view showing the whole washer inspecting apparatus using an inclined track conveyor method for supplying washers as shown in Figure 29. Figure 24 is a cross-sectional view on line J' - J' in Figure 23, and Figure 25 is an enlarged view of the inspection part A in Figure 23. The apparatus supplies and conveys washers 12 from the parts feeder 11 by means of an inclined track 22, the washers being aligned in an inclined posture in the parts feeder 11. Along the track 22, the inspecting part A is provided, where a CCD camera 23 takes in an image of the external shape of the washers 12 in the direction of a plan view, and the image processing unit 24 analyses and recognises the image and then determines the external shape and dimensions of the washers 12.

By disposing a CCD camera 21 also in the direction of side view of the washers 12, the apparatus is composed so as to inspect dimensions and features of shape such as thickness, flatness and the like at the same time, and automatically reject a defective or foreign washer according to the inspection result.

Figure 26 is a cross-sectional view on line E-E in Figure 23 and shows the cross-sectional shape of the inclined track 22. By using a CCD camera in the inspection part, the apparatus does not need a separating gate for separately conveying the washers 12 and a posture adjusting gate for conveying the washers 12 in a constant posture and can keep uniform the cross-sectional dimensions of the inclined track 22, so the apparatus can convey the washers 12 without clogging.

The apparatus is a washer supplying apparatus by means of the inclined track 22 in the parts feeder 11, as described above, can convey many kinds of washers varying in outer diameter, inner diameter, the number of teeth and the like, and can inspect them without any posture adjusting gate for keeping the washers 12 in a constant posture and any separating gate and furthermore can remove clogging of the washers.

The following arrangements are made to inspect the washers in the course of conveying them on the inclined track.

Firstly, the inclined track maintains the washers 12 at an inclination of 50 degrees, allows them to be inspected while being conveyed, and conveys them to the unacceptables ejecting outlet 25 while keeping them in the same posture after the inspection. The inspection part A has two CCD cameras 21 and 23 for the washers.

The CCD camera 23 is disposed in the direction perpendicular to the flat face of the washers 12, and a two-dimensional light-emitting illuminator 26 is disposed facing the CCD camera 23 with the washers between them. The inspection part A uses also an inclined track conveyor, whose inclined track 22 has a window number 32 of tempered glass or the like at the inspection area. The CCD camera 23 takes an image of the washer 12 with the light being transmitted through the glass member from the twodimensional light-emitting illuminator 26. Another CCD camera 21 having a ring illuminator 33 for making down-lighting makes it possible to inspect thickness and flatness by being disposed in the direction of side view of the washer 12.Another embodiment can judge a colour of the surface of the washer 12 or recognise letters on the surface of it and can be used for various applications by having the inspecting part composed of a colour CCD camera 51 and a ring illuminator 52 making down-lighting from the colour CCD camera 51 side.

Secondly, an ejecting method is adopted in which, as shown in Figure 28 (as detailed cross-section on line the K'-K' in Figure 23), only acceptable washers out of washers inspected by the image processing unit 24 in the inspecting part A are blown off by the air nozzle 27 and ejected to the acceptables ejecting chute 28 to put in the acceptables bin 29 (refer to Figure 23). When the image processing unit 24 detects a defective or foreign washer, the air of the air nozzle 27 is stopped and the defective or foreign washer is conveyed to the unacceptables ejecting outlet 25 by means of the inclined track 22 and then ejected into the unacceptables bin 30 (refer to Figure 23).In this case, since there is a time difference between the time that the inspecting part A takes in an image and the image processing unit 24 detects a defective or foreign washer and the time that the air of the air nozzle 27 is stopped, the defective or foreign washer and acceptable ones are being conveyed together mixed with each other on the inclined track 22 between the inspecting part A and the air nozzle 27.Then, by setting the time when the air nozzle is ineffective as a period long enough for the defective or foreign washer to pass by the air nozzle 27, and in particular, by setting the time when the air nozzle is ineffective so as to convey the defective or foreign washer together with one or two acceptable washers ahead of and behind the defective or foreign washer to the unacceptables ejecting outlet 25, the embodiment can eliminate the possibility that a defective or foreign washer is mixed in with acceptable ones without the necessity of identifying only a single defective or foreign washer and the necessity of controlling exactly the timing of the air nozzle 27.

By blowing off acceptable washers by the air and ejecting them out in the direction approximately perpendicular to the conveying direction of the inclined track 22, the embodiment can reduce the possibility that a defective or foreign washer is mixed in acceptable ones, since the defective or foreign washer is not ejected into the acceptables pocket 28 even if the air is insufficient or shut off, for example, due to a failure in an electromagnetic valve or the like.

In the inspecting method using the image processing unit 24, the devices described in the following are made.

1) A camera with a shutter has been used as the CCD camera so as to take in a static image even during vibration or conveyance.

2) The image processing unit generates in itself timing signals for taking images with the CCD camera and progresses consecutively and repeatedly through the steps of image taking, processing and inspecting by issuing a trigger signal for taking in the next image immediately after having taken in, analysed and recognised the previous image (this method is referred to as an internal trigger method).

3) All washers conveyed by means of the inclined track can be inspected even if they are not kept in a constant posture.

4) Inspection can be made even if an image the CCD camera has taken in contains several washers.

Figure 29 shows inspection features of the external shape of a washer tested by the image processing unit, which inspects washer outer diameter dl, teeth inner diameter d2, washer inner diameter d3, number of inner teeth s, thickness, and flatness. By using a colour CCD camera as the CCD camera, inspection of the colour, letters and the like also can be made.

Figures 30 and 31 are a flowchart of recognition and inspection of the shape of a washer 12 in the direction of a plan view in the image processing unit 24, and Figures 32A to 32J, which are its model drawings, show a field of vision F of the camera 23.

Figure 32A shows a state where two washers have been taken into the field of vision F, where a black part of the image 91 is hatched and a white part of the image 92 is not. A method of processing them is described in the following.

1) Method of extracting the number of washers in the field of vision F of the CCD camera 23 1 A raw image is taken in by the CCD camera and is converted into a 2level image by a threshold value for making a black and white 2 levels image (step 801 in Figure 30, and Figure 32A).

2 Noise 93 is removed by morphological expansion and contraction processing (step 802 in Figure 30, and Figure 32B).

3 The apparatus counts the number of black parts 94 surrounded by white parts 92 in the image and determines it as the number of the washers (step 803 in Figure 30, and Figure 32B).

2) Processing method for finding the outer diameter of a washer 1 The apparatus finds the centre of gravity of each of the n black parts 94, (where n is the number of the washers found in 3 of 1), and determines it as the centre of gravity a of each of the washers (step 804 in Figure 30, and Figure 32C).

2 I is initialised (step 805).

3 I and the number of washers n are compared with each other, and if I is less than the number of washers n, step 807 in Figure 30 is performed, and if I is not less than the number of washers n, step 870 is performed and the result is outputted (step 806 in Figure 30).

4 The apparatus finds points b and c at which the vertical line 1 passing through the centre of gravity of the washer a and the circumference of the washer K intersect with each other, and sets the length of the segment b-c linking the points of intersection as the washer outer diameter dl (step 807 in Figure 30, and Figure 32D).

5 The washer outer diameter dl and a reference value set in advance are compared with each other, and if the washer outer diameter dl satisfies the reference value, step 809 in Figure 30 is performed and if it does not satisfy, the process goes to step 850 in Figure 31 to determine the washer as an unacceptable one (step 808 in Figure 30).

3) Processing method of finding the number of inner teeth 1 Taking the centre of gravity of the washer a as a reference point, the processing unit makes a logical operation (conjunction) between the washer image screen and a reference window screen (Figure 32E), and apparently reduces the washer outer diameter dl and makes thin the washer width t to make the teeth easy to extract (step 809 in Figure 30, and Figure 32F).

2 The inner tooth parts f are extracted through morphological expansion and contraction processing (Step 810 in Figure 30, and Figure 32G).

3 The processing unit counts the number of the inner tooth parts f and sets it as the number of inner teeth s (Step 811 in Figure 30, and Figure 32G).

4 The number of inner teeth s and a reference value set in advance are compared with each other, and if the number of inner teeth s is the same as the reference value, Step 813 in Figure 30 is performed, and if it is not the same, the process goes to Step 850 in Figure 31 to determine the washer as an unacceptable one (Step 812 in Figure 30).

5 The processing unit finds the centre of gravity g of each of the inner tooth parts f (Step 813 in Figure 31, Figure 32G).

6 The processing unit draws a line 2 passing through the centre of gravity of an inner tooth g and the centre of gravity of the washer a, finds points h and j at which the line 2 and inner teeth in the image in Figure 32F intersect with each other, and determines the length of the segment h-j linking the points of intersection as the teeth inner diameter d2 (Step 814 in Figure 31, and Figure 32H).

7 The teeth inner diameter d2 and a reference value set in advance are compared with each other, and if the teeth inner diameter d2 satisfies the reference value, Step 816 in Figure 31 is performed, and if it does not satisfy, the process goes to Step 850 in Figure 31 to determine the washer as an unacceptable one (Step 815 in Figure 31).

5) Method of finding the inner diameter of a washer 1 The processing unit makes a line 3 by revolving the line 2 around the centre of gravity of the washer a by angle e set in advance (Step 816 in Figure 31, and Figure 32J).

2 The processing unit finds points u and m at which the line 3 and the washer inner contour of the image in Figure 32F intersect with each other, and determines the length of the segment u-m linking the points u and m of intersection as the washer inner diameter d3 (Step 817 in Figure 31, and Figure 32J).

3 The washer inner diameter d3 and a reference value set in advance are compared with each other, and if the washer inner diameter d3 satisfies the reference value, Step 820 in Figure 31 is performed, and if it does not satisfy, the process goes to Step 850 to determine the washer as an unacceptable one (Step 818 in Figure 31).

4 The processing unit determines a washer as an acceptable one (Step 819 in Figure 31).

6) Method of finding the washer outer diameter dl, the number of inner teeth s, the teeth inner diameter d2, and the washer inner diameter d3 of n washers in the field of vision F 1 1 is added to I (Step 820 in Figure 31).

2 The processing unit repeats Steps 806 and 820 in Figures 30 and 31 by n times where in n is the number of the washers found in Step 803 in Figure 30 and thus finds the washer outer diameter dl, the number of inner teeth s, teeth inner diameter d2, and washer inner diameter d3 for each of a washers in the field of vision.

7) Output of the result 1 The result whether the washer is acceptable or unacceptable is outputted (Step 870 in Figure 30).

2 If a stop signal has been entered, the process goes to Step 872 in Figure 30, and if it has not been entered, the process goes to Step 801 in Figure 30 and takes in the next image (Step 871 in Figure 30).

3 The process is stopped (Step 872 in Figure 30).

The above is the image processing method in the direction of a plan view. Next, an image processing method in the direction of side view is described.

Figure 33 is a flowchart of recognition and inspection of the shape of a washer 12 from a side view, and Figures 34A, 34B and 34C are its model drawings. Figure 34A shows a state where washers 111, 112, 113 and 114 have been taken into the field of vision V of the CCD camera 21, where a black part of the image 115 is hatched and a white part of the image 116 is not. A method for processing them is partly described in the following.

1) Method of extracting image data of washers 12 in the field of vision V of the CCD camera 21 1 A raw image is taken in by the CCD camera 21 and is converted into a 2level image by a threshold value for making a black and white 2 levels image (Step 1001 in Figure 33, and Figure 34A).

2 The number of black pixels each of which has the same value of the x coordinate is counted for each pixel point on the x co-ordinate in the field of vision V, and a graph of x vs. number of pixels is obtained (Step 1002 in Figure 34B).

2) Method of inspecting the maximum value of thickness h of washers in the field of vision V of the CCD camera 21 1 n and X are initialised (Step 1003 in Figure 33).

2 The number of black pixels each of which has the same value of the x coordinate is counted for each pixel point on the x co-ordinate as beginning with XO in the direction of the x axis (Step 1004 in Figure 33, and Figure 34C).

3 The number of black pixels and an upper limit set in advance are compared with each other for each pixel point on the x co-ordinate, and if any number of black pixels does not exceed the upper limit, the process goes to Step 1006 in Figure 33 and if some number of black pixels exceeds the upper limit, the process goes to Step 1100 in the Figure 33 to determine the washer as an unacceptable one (Step 1005 in Figure 33).

3) Method of inspecting the minimum value of thickness h of washers 12 in the field of vision V of the CCD camera 21 1 The number of black pixels each of which has the same value of the x coordinate is counted for each pixel point on the x co-ordinate as beginning with X0 in the direction of the x axis (Step 1006 in Figure 33, and Figure 34C).

2 The number of black pixels and a lower limit set in advance are compared with each other for each pixel point on the x co-ordinate, and if any number of black pixels does not fall below the lower limit, the process goes to Step 1008 in Figure 33 to determine the washer as an acceptable one and if some number of black pixels falls below the lower limit, the process goes to Step 1050 in the Figure 33 (Step 1007 in Figure 33).

3 The processing unit judges whether the value less than the lower limit is zero or not, and if it is zero, the process goes to Step 1051 in Figure 33 and if it is not zero, the process goes to Step 1100 in Figure 33 to determine the washer as an unacceptable one (Step 1050 in Figure 33, and Figure 34C).

4 1 is added to n (Step 1051 in Figure 33).

5 An x co-ordinate of the pixel point where the number of black pixels has become zero is set as X1 (Step 1052 in Figure 33, and Figure 34C).

6 The number of black pixels each of which has the same value of the x coordinate is counted for each pixel point on the x-co-ordinate as beginning with X1 in the direction of the x axis (Step 1053 in Figure 33, and Figure 34C).

7 The processing unit judges whether or not there is the number of black pixels greater than zero, and if there is, the process goes to Step 1055 in Figure 33 and if there is not, the process goes to Step 1008 in Figure 33 to determine the washer as an acceptable one (Step 1054 in Figure 33).

8 1 is added to n (Step 1055 in Figure 33).

9 an x co-ordinate of the pixel point where the number of black pixels has become greater than zero is set as X2, the process goes to Step 1006 in Figure 33, and such an operation as this is repeated to the end of the field of vision (Step 1056 in Figure 33).

3) Output of the result 1 The result whether the washer is acceptable or unacceptable is outputted (Step 1200 in Figure 33).

2 If a stop signal has been entered, the process goes to Step 1202 in Figure 33, and if it has not been entered, the process goes to Step 1001 in Figure 33 and takes in the next image (Step 1201 in Figure 33).

3 The process is ended (Step 1202 in Figure 33).

In the above, methods for inspecting washers and the like which can be conveyed by means of an inclined track have been described, but the methods can be also applied to other plate-shaped parts (for example washers, electric parts, other processed parts, and the like) and block-shaped parts (for example nuts, IC packages, and the like).

As described above, since the invention adopts a supplying and arranging method by means of a one-side hanger chute, V-grooved chute, inclined track and the like, uses an inspecting unit have a built-in image processing unit which controls image taking devices and makes an image analysis and image judgement, and uses a method of blowing as described the following advantages accrue: 1 Parts can be inspected regardless of their colour or external shape.

2 Parts can be inspected without being affected by speed change caused by vibration or sliding during conveyance of the part to be inspected, in contrast with former methods.

3 By disposing plural CCD cameras, the invention makes it possible to judge the shape, dimensions, colour, letters, and coloured letters of parts to be inspected in the directions of its plan view and side view, and furthermore makes these operations possible by means of one image processing unit.

4 By making all inspection and analysis of the shape and the like of parts by means of image taking devices and an image processing unit, the invention has made it unnecessary to supply independently the parts to be inspected to an inspection part and has removed a cause of clogging of parts to be inspected so the invention has made possible continuous inspection over a long time, has made the whole inspection apparatus compact, and has made replacement and adjustment of parts of the apparatus unnecessary.

5 By adopting a method of blowing acceptable parts off the conveyer track to classify acceptable and unacceptable parts after inspection of the parts, the invention has made it possible to prevent unacceptable parts being mixed in acceptable ones.

Claims (20)

1. Apparatus for inspecting step-shaped parts comprising means for supplying and arranging parts, means for conveying parts, means for inspecting parts, image processing means, and means for ejecting parts, wherein: the means for supplying and arranging parts has a one-side hanger guide widening toward its downstream end, the means for conveying parts has a one-side hanger chute conveying the parts placed in a one-side hanging posture by the one-side hanger guide, the means for inspecting part has at least one image pickup device out of an image pickup device taking an image of either the plan view or the side view of the parts to be inspected, the image processing means has an image processing unit which is connected with the image pickup device and inspects and determines the shape and the like of parts to be inspected by processing and analysing an image of them, and the means for ejecting parts has an ejecting unit which ejects the parts as acceptable parts and unacceptable ones on the basis of signals generated by the image processing unit.

2. Apparatus as claimed in Claim 1, wherein the one-side hanger chute has a transparent part transmitting light illuminating parts to be inspected so that the image pickup device may take an image of them.

3. Apparatus as claimed in Claim 1, wherein the image processing unit has a timing means for consecutively taking an image of the parts in the inspecting means by generating a signal to take in the next image just after taking in, analysing and judging a previous image taken by the image pickup device.

4. Apparatus as claimed in Claim 1, wherein the means for ejecting parts has an air nozzle blowing an inspected part the image processing unit has determined as an acceptable part off the conveyance path of the conveying unit.

5. Apparatus for inspecting parts comprising means for supplying parts, a means for arranging and conveyingvparts, means for inspecting parts, image processing means, and means for ejecting parts, wherein: the means for supplying parts has a unit controlling a quantity of parts to be supplied for inspection, the means for arranging and conveying parts has a V-grooved chute whose slants forming the V-groove becomes gradually lower in height toward its downstream end, the means for inspecting parts has at least one image pickup device out of an image pickup device taking an image of either the plan or side view of the parts to be inspected, the image processing means has an image processing unit which is connected with the image pickup device and inspects and determines the shape and the like of parts to be inspected by processing and analysing an image of them, and the means for ejecting parts has an ejecting unit which ejects the parts as acceptable parts and unacceptable ones determined by the image processing unit.

6. Apparatus as claimed in Claim 5, wherein the V-grooved chute has transparent part transmitting light onto parts to be inspected so that the image pickup device may take an image of them.

7. Apparatus as claimed in Claim 5, wherein the image processing unit has a timing means for consecutively taking an image of the parts placed in the inspecting means by generating a signal to take in the next image just after taking in, analysing and judging a previous image taken by the image pickup device.

8. Apparatus as claimed in Claim 5, wherein the means for ejecting parts has an air nozzle blowing an inspected part the image processing unit has determined as an acceptable part off the conveyance path of the conveying unit.

9. A method of inspecting step-shaped parts comprising: (A) placing parts to be inspected in a one-side hanging posture, (B) conveying the parts to be inspected in a one-side hanging posture having a specified inclination, (C) taking images of the parts in the course of conveyance by means of an image pickup device, (D) processing and analysing the images and determining the parts to be acceptable or unacceptable, and (E) ejecting the parts as acceptable parts and unacceptable ones.

10. A method as claimed in Claim 9, wherein the step of processing and analysing the images comprises: (F) taking in an image from an image pickup device and converting it into a 2level image, (G) making an expansion or contraction of the image by means of morphology, (H) performing an exclusive-OR operation between both images obtained in the processes (f) and (g), (I) detecting specified points on lines set in advance and measuring the respective dimensions, and (J) making a determination by comparing the result obtained in step (i) with an image ofan acceptable part prepared in advance.

11. A method of inspecting parts comprising (a) controlling the quantity of parts to be inspected, (b) arranging and conveying the parts to be inspected, (c) taking images of the parts to be inspected in the course of conveyance by means of an image pickup device, (d) processing and analysing the images and determining the parts to be acceptable or unacceptable, and (e) ejecting the parts as acceptable parts and unacceptable ones.

12. A method as claimed in Claim 11, wherein the step of processing and analysing the images comprises: (f) taking in an image from an image pickup device and converting it into a 2level image, (g) making an expansion or contraction of the image by means of morphology, (h) performing an exclusive-OR operation between both images obtained in the processes (f) and (g), (i) detecting the respective points on lines set in advance and measuring the respective dimensions, and (j) making a determination by comparing the result obtained in step (i) with an image prepared in advance of an acceptable part.

13. Apparatus for inspecting parts comprising means for supplying and arranging parts, means for inspecting parts, and means for ejecting parts, wherein: the supplying and arranging means has an inclined track, the inspecting means has at least one image pickup device for taking an image of either the plan or side views of parts to be inspected and an image processing unit connected with the image pickup device for processing an image, inspecting and determining the shape, colour and the like of the parts to be inspected on the basis of the processed images obtained by the image processing unit, and the ejecting means ejects the inspected parts the image processing unit has determined to be acceptable.

14. Apparatus as claimed in claim 13, wherein the inclined track has an opening in which a transparent member is fitted and the image pickup device takes an image of parts to be inspected made by light from an illuminator falling onto the parts placed on the opening through the transparent member.

15. Apparatus as claimed in claim 13, which has an image pickup means comprising an image pickup device and an illuminator making down-lighting from the image pickup device side and which takes a reflected image of parts obtained.

16. Apparatus as claimed in claim 13, wherein the image processing unit has a timing signal generating means for generating a timing signal for the image processing unit to take the next image into an image pickup device according to its image processing software after taking in, analysing and recognising an image picked up by the image pickup device.

17. Apparatus as claimed in claim 13, wherein the acceptable ejecting means has an air nozzle which is provided on the lower part of the inclined track in the direction approximately perpendicular to the direction of travel of the parts and blows outwardly off the inclined track approximately perpendicularly to it, the inspected parts the image processing unit has determined as acceptable by means of the air.

18. A method of inspecting parts comprising: (a) arranging and conveying parts to be inspected which have been supplied from a parts supplying unit by means of an inclined track, (b) taking an image of parts to be inspected in the course of being conveyed on a conveyor track by means of an image pickup device, (c) separating picked up images into individual images, (d) recognising the shape, colour, letters and the like of parts and determining the parts to be acceptable or unacceptable, and (e) ejecting the inspected parts determined to be acceptable.

19. Apparatus for inspecting parts substantially as hereinbefore described with reference to and as shown in any one of the accompanying Figures 1 to 20 and 23 to 34.

20. A method of inspecting parts substantially as hereinbefore described with reference to any one of the accompanying Figures 1 to 20 and 23 to 34.