WO1987001976A1

WO1987001976A1 - Optical discrimination method for component orientation

Info

Publication number: WO1987001976A1
Application number: PCT/GB1986/000564
Authority: WO
Inventors: Cyril Kenneth Edwards
Original assignee: Ariel Industries Plc
Priority date: 1985-09-30
Filing date: 1986-09-22
Publication date: 1987-04-09
Also published as: JPS63500921A; EP0238534A1

Abstract

A method of orienting a stream of components, which components can assume any one of a small number of different stable orientation and have distinguishing features on one or more portions comprising: arresting the motion of a said component and positioning it in relation to an incident beam of light so that said beam illuminates a local area within the component where a distinguishing feature will lie if the component is in a predetermined orientation, and monitoring the transmitted or reflected beam by photodetector means, said monitoring being synchronised with the positioning of the component to obtain an output from said photodetector means which is dependent substantially only on said local area; and using the output of said photodetector means to detect the orientation of the component and to effect any necessary reorientation to bring it into a desired orientation, or to segregate it from other components which have the desired orientation.

Description

"Optical discrimination method for component orientation"

Our invention relates to an optical discrimination method and means for component orientation.

Many industrial operations involve the processing or the assembly of engineered components. Frequently the components concerned have to be fed one at a time in a single line to an input point- with each component assuming a specified orientation. The geometry of most components is such that they can be brought into a single in-line stream without difficulty and there are well-established means, such as vibratory bowl feeders, for doing this. However, if the components concerned can assume two or more stable in-line orientations and one or more of these is unacceptable at the next processing stage the problem becomes more difficult and frequently cannot be adequately coped with by a bowl feeder. Vibratory bowl feeders normally depend upon mechanical tooling positioned along the flightways to ensure that only components lying in a desired orientation within an in-line stream can reach the input point at the next component processing stage. Such an arrangement has two principal limitations: firstly, mechanical tooling can differentiate between components lying in various orientations only if the features which distinguish the orientations are mechanically detectable, and often they are not; secondly, it is seldom possible by means of mechanical tooling to re-orientate components which are not in a desired orientation. Each stage of mechanical tooling normally operates by rejecting and returning to the well of the bowl feeder any components lying in one of the undesired orientations. Where the geometry of the components is such that a high proportion is rejected because of undesired orientation the feed rate is seriously reduced, particularly in applications where there is a need for several tooling stages and hence several stages of rejection.

One method of overcoming this problem is the use of optical discrimination. It is based upon the well-known fact that the pattern of light which is reflected by a component when it is illuminated differs according to the surface features of the portion of the component which is illuminated and hence that by monitoring the reflected light it is possible to determine in which orientation the component is lying. It has been found in practice that even when the surfaces of the component are not truly reflective the patterns of light scattered or reflected by those surfaces are frequently sufficiently distinctive to enable the orientation of the component to be determined. (The terms "optical" and "light" are used herein to include a wide range of electro¬ magnetic radiations extending from ultra-violet through visible radiation to infra-red and radio or micro-waves.)

Optical systems overcome the principal limitations of mechanical discrimination, firstly because they are more versatile and are not dependent upon the surfaces being mechanically distinguishable; and secondly because the light received from the component can readily be turned into a signal which can be used to activate a reorientation device thereby providing a continuous stream of correctly orientated components without reducing the flow rate.

GB-A-2,116,706 describes one particular method of using optical discrimination. It describes a system wherein the component is temporarily illuminated by a beam of light as a result of relative movement occurring between the component and the beam and wherein the orientation in which the component lies is determined by monitoring the response profile generated in a photoelectric detection system by the light scattered or reflected by surface features of the component. In practice this method has limited applicability, firstly because it provides no ready means for coping with the situation which arises when a stable mode for transporting the component is not the optimum one for inspection purposes and, secondly, it provides no ready means for segregating the response received from features which distinguish the orientation from the response received from those features which are common to two or more orientations. It therefore requires the use of complex equipment for signal analysis to isolate that part of the response which is associated with a distinguishing feature, or alternatively it requires the light source and receiver to be so positioned that the response from a distinguishing feature is always greater than that received from any other feature so that the distinguishing feature can be identified purely by signal amplitude. This latter requirement has proved to be extremely restrictive. Even where it is achievable it often requires the light source and receiver to be so positioned that the response from the distinguishing feature is far from optimal.

We have now discovered that these problems can be overcome by momentarily arresting the motion of the component at the point of inspection. By this means, firstly, the illumination of the component can be restricted to the local area within which distinguishing features may lie thereby obviating the need to segregate signals generated by distinguishing features from those generated by non-distinguishing features; secondly the component can be positioned relative to the light source and receiver so that the optimum response is received; thirdly, where necessary, the orientation of the component can be modified at the point of inspection to cope with the situation where distinguishing features are inconveniently positioned. For instance they frequently lie on the surface on which the component rests when in a stable orientation for transport, and when this occurs it is necessary to reorientate the component to bring the area which may contain a distinguishing feature to a position where it can be illuminated; fourthly, the response can be maintained long enough to generate a reliable signal. Furthermore this method is versatile enough to allow multi-positioning of a component or the use of multiple light sources to cope with a situation where the distinguishing feature or features do not all lie within one local area.

In one aspect our invention provides a method of orienting a stream of components, which components can assume any one of a small number of different stable orientations and have distinguishing features on one or more portions, comprising: arresting the motion of a said component and positioning it in relation to an incident beam of light so that said beam illuminates a local area within the component where a distinguishing feature will lie if the component is in a predetermined orientation, and monitoring the transmitted, scattered or reflected beam by photodetector means, said monitoring being synchronised with the positioning of the component to obtain an output from said photodetector means which is dependent substantially only on said local area; and using the output of said photodetector means to detect the orientation of the component and to effect any necessary reorientation to bring it into a desired orientation, or to segregate it from other components which have the desired orientation.

The present invention overcomes the limitations inherent in the known system based upon interpreting the response profiles of the reflected or scattered light as successive areas of components are illuminated in sequence as they pass through a light beam. The method of our invention thus only monitors signals from the local area within which distinguishing features may lie. The movement of the component is arrested by suitable stop means prior to monitoring. It is preferred to bring the component into such a position relative to the light source and photodetector that the change in output signal from the photodetector according to whether or not a distinguishing feature is present within the local area is substantially optimised.

For instance, the components may be fed onto a conveyor band through a metering device which works in synchronism with both the travel of the conveyor band and with the positioning of a shutter in front of a photo-electric receiver. With this arrangement the metering device will feed the components accurately into spaced positions along the conveyor band and the shutter will blank off the aperture of the photo-electric receiver until each component in turn is arrested and so positioned that the local area which may contain a distinguishing feature is illuminated by the light source. Simultaneously with the component arriving in this position the shutter will be withdrawn allowing reflected or scattered light from the local area to generate a signal in the photo-electric receiver. Immediately a signal is received from the local area the shutter will be replaced thereby preventing signals being received from features in other areas. In many instances it will be preferable to synchronise the monitoring and component position by means of electrical or electronic switching thereby removing the need for mechanical shuttering. Positioning mechanisms are used to bring components

into the desired position relative to the light source and photodetector. These mechanisms will momentarily bring the components to rest and may move them in any direction relative to the conveyor band necessary to enable the optical system to provide a reliable signal.

Sometimes it is feasible and convenient for the aforesaid metering device to serve also as a positioning mechanism, i.e. the components may be monitored at the moment they are being metered. If desired, two or more local areas of said component may be monitored to detect its orientation about two or more axes.

In order to monitor only the desired local area of the component one may either confine the illumination to a narrow beam carefully positioned to pick out the desired area, or one may use more diffuse illumination in conjunction with a photodetector accurately aligned on the desired area. As can be seen, our invention neatly avoids the problem of having to segregate signals generated by distinguishing features from those generated by non-distinguishing features. It gives complete freedom for positioning the light source and receiver related to the component so that they can be placed where the optimum response will be received. It ensures that the response can always be maintained long enough to generate a reliable signal. It allows the component to be positioned precisely relative to the light source and receiver and, where necessary, allows the orientation of the component to be modified during the period of illumination so that a confirmatory check on its orientation may be made. Futher ore it is versatile enough to allow multiple positioning of a component or the use of multiple light sources to cope with the situation where the distinguishing feature or features do not all lie within one local area.

Thus another aspect of our invention is a means for orienting a stream of components, which components can assume any one of a small number of different stable orientations and have distingushing features on one or more local areas, comprising: a light source and photodetector; means for arresting the motion of a said component and positioning it in relation to said light source and photodetector; means for monitoring the output from said photodetector in synchronism with the positioning of the component to obtain an output from said photodetector which is dependent substantially only on a determined local area of said component where a distinguishing feature will lie when the component is positioned; and means responsive to said output to effect a desired reorientation of the component or to segregate it from other components which have the desired orientation.

Our invention is illustrated diagrammatically by way of example only with reference to the accompanying drawings, wherein:-

Fig 1.- is a perspective view of an apparatus for carrying in-line components through three optical test stations.

Fig 2 is a view of a typical component in its four possible orientations.

Fig 3 shows the same component and defines the local areas where the component must be illuminated to determine its orientation.

The requirement in this example is to present the components to the input stage of the next operation with the distinguishing feature (in this case a V-notch) on the leading edge and above the centre line of the component (as drawn) . This is achieved in two stages. In the first stage the component is checked to determine where or not the notch lies on the trailing edge. A local area 10 (Fig 3) on the trailing edge which encompasses the position where the notch will lie if it is on the trailing edge either above or below the centre line is illuminated, so that if a notch is present a turn-around device can be activated to bring the notch to the leading edge. In the second stage the component is checked to determine whether or not the notch, which is now always on the leading edge, is above or below the centre line. This is achieved by illuminating a local area 14 (Fig 3) on the leading edge where the notch will lie if it is below the centre line, so that if a notch is present a turn-over device is activated to bring the notch above the centre line.

Referring now to Fig 1, the apparatus comprises a conveyor belt 1 with a drive shaft 2 running to one side. The drive shaft actuates a metering device 3, and positioning mechanisms 4, 5, 6 and 7. The drive shaft is geared to the drive of the conveyor belt through bevel gearbox 28 and pulleys 29 so that the metering device and positioning mechanisms can be actuated in synchronism with the travel of the conveyor belt. Moreover the encoder 26 produces a digitised output dependent on the rotation of shaft 2. The output is fed to a controller (not shown) which is thereby enabled to energise positioning mechanisms 4, 5, 6 and 7 at the appropriate times. A single in-line stream of components 8 emerges from bowl feeder 17 and enters guide 18 in random orientation. The stream is carried by the conveyor belt to the metering device 3 which regulates the flow of the components by releasing them one at a time and accurately spacing them along the belt. Each spaced component is carried by the belt to positioning mechanism 4 which brings the component into the correct position for illumination by a light source 9 which projects a beam of light onto a local area 10 (Fig 3) on the trailing edge of the component. A convenient light source for use in this invention is an 0.5 mW helium-neon laser, but light sources extending over a wide range of electro-magnetic radiations have been used successfully. The light reflected from the illuminated area is received by a phototransistor 12 which is incorporated into a conventional detector circuit whose output is monitored only where the component has been arrested by positioning device 6. The output is applied to a first input of a voltage comparator, to a second input of which is applied a preset voltage derived from a constant voltage source. The voltage comparator is set to generate an output signal if, and only if, the voltage applied to the first input exceeds that applied to the second input. The output signal on line 30 is used to actuate the solenoid 11 of a turn-around device 27 if the pattern of reflected light indicates that the notch is on the trailing edge of the component. Positioning mechanism 4 is then mechanically withdrawn by cam 19 and bell crank 20 and the component is allowed to proceed along the conveyor belt to positioning mechanism 5 which retains the component in the correct position for illumination by light source 13, which projects a beam of light onto a local area 14 (Fig 3) on the leading edge of the component. The light reflected from the illuminated area is received by a phototransistor 15 which actuates a turn-over device 16 by a signal on line 31 to solenoid 25 if the pattern of reflected light indicates that the notch is within the illuminated area. During this operation the movement of the component is arrested by positioning mechanism 6.

Positioning mechanism 6 is then mechanically withdrawn and the component allowed to proceed along the conveyor belt. All components arriving at this stage will have passed through both optical tests, and any necessary reorientations should have been effected so that all components will lie in the desired orientation. A final check is made at the third optical test station comprising positioning mechanism 7, light source 22 and photodetector 23. Any mis- oriented components are removed from the conveyor by a signal on line 32 to rejector means powered by solenoid 25. The third test station is only necessary if a very high integrity of the output components is needed, and in practice the rejector means will very seldom be activated.

Claims

1. A method of orienting a strea'm of components, which components can assume any one of a small number of different stable orientations and have distinguishing features on one or more portions comprising: arresting the motion of a said component and positioning it in relation to an incident beam of light so that said beam illuminates a local area within the component where a distinguishing feature will lie if the component is in a predetermined orientation, and monitoring the transmitted or reflected beam by photodetector means, said monitoring being synchronised with the positioning of the component to obtain an output from said photodetector means which is dependent substantially only on said local area; and using the output of said photodetector means to detect the orientation of the component and to effect any necessary reo ientation to bring it into a desired orientation, or to segregate it from other components which have the desired o ientation.

2. A method according to claim 1 wherein two or more local areas of said component are monitored, to detect the orientation of said component about two or more axes.

3. A method according to claim 1 or 2 wherein prior to said monitoring, the orientation of said component is modified to improve the visibility of said distinguishing feature to said photodetector means.

4. Means for orienting a stream of components, which components can assume any one of a small number of different stable orientations and have distinguishing features on one or more local areas, comprising: a light source and photodetector; means for arresting the motion of a said component and positioning it in relation to said light source and photodetector; means for monitoring the output from said photodetector in synchronism with the positioning of the component to obtain an output from said photodetector which is dependent substantially only on a determined local area of said component where a distinguishing feature will lie when the component is positioned; and means responsive to said output to effect a desired reorientation of the component or to segregate it from other components which have the desired orientation.

5. Means according to claim 4 including means for monitoring two or more local areas of said component, to detect its orientation about two or more axes.

6. Means according to claim 5 comprising a turn¬ around device and a turnover device for correcting the orientation of said component about two axes.