GB2186359A - Automatically and accurately positioning a workpiece - Google Patents

Abstract

A method of automatically and accurately positioning a first workpiece in a set position relative to a second workpiece (11) comprises the steps of engaging a tool (22) with the first workpiece, moving the first workpiece and tool to a datum position, receiving light from the second workpiece and the tool in an electronic camera (30), electronically analysing the signal produced by the eletronic camera to accurately determine the position or relative position of both the second workpiece (11) and the tool (22), and moving the first workpiece to the set position so that any inaccuracies in the movement of the tool (22) can be monitored. The sensing by the camera is improved by a reflector to receive light reflected from (Fig. 5) or just missing (Fig. 6) the edge of the first workpiece, or by a filter to single out a bright spot produced by reflection from that edge (Fig. 8). <IMAGE>

Description

SPECIFICATION Automatically and accurately positioning a workpiece This invention relates to an improvement to the invention discribed in our previous application numbered 8521156 filed on the 23rd August 1985 (hereinafter referred to the "previous Application") a copy of the text ofthe specification of which is appended hereto at pages numbered 5 to 18 and the drawings for which are identical to the drawings offigures 1 to 4 of this specification.

The subject matter of the previous application is thus incorporated into this specification and only the modifications to the original arrangement will be described.

In the previous Application a preferred arrangement is described in which light is received in an electronic camera from a first workpiece which comprises a glass panel, simultaneously with light being received from a second workpiece i.e. a body part of a vehicle which has an aperture to receive the glass panel, and a tool which comprises a carrier or gripperwhich carries the glass panel, at a datum position.

The light received from the first and second workpieces determines the relative positions of the first and second workpieces in orderthatthe panel can be accurately placed in the aperture. Thus the positions ofthe edges ofthe panel and the aperture is determined.

It has been found that where the glass panel is scrupulously clean, it is not always possible to receive a satisfactory image by the electronic camera, of the edge oftheglass panel. The problem is aggravated where the glass panel has an edge band which is usually biack or dark coloured, which is required to conceal the periphery ofthe aperture ofthe body part immediately beneath the edge of the panel, in arrangements which do not have a rubber seal around the periphery of the panel, but rely on adhesive between the panel and the body partto provide an adequate seal.

Accordinglythree alternative ways have been advised to overcome this problem.

In a first arrangement, a ground glass, opaque plastic or other screen is positioned between the first workpiece and the electronic camera. When correctly positioned, the screen receives light reflected from the edge ofthe firstworkpiece and provides an enhanced image which can readily be viewed by the electronic camera. Thus the light from the first workpiece is deflected by the screen to the electronic camera.

Preferably, the screen is placed between the first workpiece and the camera a known distance from the firstworkpiece. In one example this may be achieved by carrying the screen with the panel, by the tool. The tool may have means to move the screen into the known position subsequentto the tool engaging with thefirstworkpiecesothatthescreendoes not interfere with the normal operation of the tool Because the computer "knows' the distance from the screen to the first workpiece, this spacing of the imagefromthefirstworkpiececan betaken into account and accommodated when determining the relative positions of the firstworkpiece, for example relative to the second workpiece.

In a second arrangement, a screen is positioned such that the first workpiece is between the screen and the electronic camera. In this arrangement, it is light which is passes the first workpiece which is received on the screen to provide an image which is viewed by the electronic camera. Again the screen may be spaced from the first workpiece between the screen and the electronic camera a known distance from the firstworkpiece, and may be carried by the tool. The tool may again move the screen into position subse quentto the tool engaging the first workpiece.

The position of the edge of the first workpiece is thus determined by the extent of the shadow of the edge of the firstworkpiece.

The dark or black edge band is usually spaced inwardly of the periphery of the glass panel a very smalldistanceforexampleintheorderofone millimetre, leaving a transparent peripheral region.

Where the light from the light source impinges upon the peripheral region, a bright dot of light is formed which may be viewed bythe electoniccamera.

In the third arrangement which has been devised, the electronic camera is provided with a low band filter so that only the brightest image is seen. Thus the camera can be adjusted to "see" the light dot reflected from the peripheral region of the glass panel only, and all other unreliable signals filtered out.

The invention will now be described with the aid of the accompaning drawings in which figures 1 to 4 are identical to the drawings filed with our previous Application; FIGURE 5 is a view similarto FIGURE 3 but showing the glass panel priorto received by the body part and illustrating the first arrangement which has been devised for overcoming the problem encounted with the previous arrangement; FIGURE 6 is a view similarto FIGURE 5 but showing the second arrangement which has be devised for overcoming the problem with the previous arrangement; FIGURE 7 is a plan view ofthe FIGURE 6 arrange mentshowingtheimagewhich is received bythe camera; FIGURE 8 is a view similarto FIGURES 5 and 6 but illustrating how the third arrangement described above operates; and FIGURE 9 is a plan view ofthe image obtained bythe camera using the arrangement of FIGURE 8.

Referring to the drawings, the arrangements shown in figures 1 to 4 are fully described in the previous Application appended hereto at pages numbered Sto 17 and hence further description is not considered required.

Referring to figure 5, like parts ofthe parts offigures 1 to 4 are labelled with the same reference numerals but with a prime sign added.

Afirstworkpiece comprises a glass panel 13' which The claims were filed later than the filing date within the period prescribed by Rule 25(1) of the Patents Rules 1982.

isto be placed in an aperture in a second workpiece 14' comprising a body part of a vehicle.

The panel 13' has an edge band 28' which extends around the entire edge ofthe panel 13' and comprises a darkorblackstaining within the glass 13'. It can be seen thatthe band 28' extends nearly up to the periphery ofthe panel 13' but there is a region R in the order of one millimetre wide between the periphery Pandthe band 28'. Afan of laser light3l is directed onto the edge ofthe panel 13' simultaneously with the light being directed onto calibration markings ofthetool carrying panel 13' as described in the previous Application, and onto the recess 34' ofthe second workpiece 14'. The light reflected from the secondworkpiece 14' andthetool (notshown in figure 5) is reflected directly backto an electronic camera 55'.However, it has been found that sufficient light is directly reflected from the edge ofthe first workpiece 13' to provide a satisfactory image in camera 55'.

This is suspected to be because of internal reflections within the band 28' ofthe glass panel 13' so that the emerging image has insufficient intensity to be seen by the camera 55' along with the other stronger images obtained from reflections from the calibration markings and the secondworkpiece 14'. Thus a screen S is positioned to receive light reflected from the edge ofthe panel,thescreen comprising a ground glass or opaque plastic screen on which an enhanced image if formed. It has been found that the image formed on such a screen is satisfactory received bythe camera 55' forthe camera 55' to sense the edge ofthefirst workpiece 13'.

Preferably, the distance from the screen S to the first workpiece 13' is accurately known so that the compu tercontrol means 25 (not shown in figure 5) which controls movementofthe robot arm (not shown in figure 5) can accurately determine the position of the edgeofthefirstworkpiece 13' for example relative to the second workpiece 14'.

Referring now to figure 6 a similar arrangement is shown andthesame reference numerals are used as in figure 5. However the screen S is not positioned between thefirstworkpiece 13' and the camera 55' but ratherthefirstworkpiece 13' is positioned between the screen S and the camera 55'. In this way, the light which passes the edge of the panel 13' impinges upon the screen S and is reflected to the camera 55' so that the position of the firstworkpiece 13' is determined in accordance with the extent of the shadow ofthe edge of the panel 13'.

The image received bythe camera 55' using the figure 6 arrangement is shown infigure7. It can be seen thatthe image ofthe edge ofthe panel 13',which is indicated at 1 is spaced slightly from the actual edge of the panel 13' but, because the distance from the screen Sto the firstworkpiece 13' is known, the computer may take into accountthis spacing in determining the relative positions ofthe first and secondworkpieces 13', 14'.

Preferably, the screen S ofthefigure 5 orfigure 6 arrangement is carried bythe tool which engages with thefirstworkpiece 13' to movethefirstworkpiece 13' to the datum position shown. The screen may be stowed in one position so as not to interfere with the normal operation ofthetoolwhen engagingthefirst workpiece 13', and may be moved to the positions shown in figure5 orfigure 6 oncethetool has engaged with the first workpiece.

Referring now to figures 8 and 9, the operation of the third arrangement described above is illustrated, again similar partstothearrangementsshown in figures Sand 6 being given the same reference numerals.

It can be seen from figure 9 thatthe dark or black edge band 28' does not extend to the periphery P, but there is a narrow peripheral region R between the band 28' and the periphery F. The region R is in the order of one millimetre wide.

In such an arrangemerit, the edge ofthe panel 13' cannot readily be seen bythe television camera 55'.

However, there is a reflection of the fan of light31' from the peripheral region R which appears as a very bright dot D, and this dot D is seen by the camera 55'.

The camera 55' and the associated control means can be arranged to "see" the dot Din order to establish where the edge of the panel 13' is. However, the camera 55' will also receive unreliable signals which may be reflected from along the edge ofthe panel 13' and from the body part 14' belowthe edge and accordingly, the television camera 55' is provided with a low band filterwhich filters out all butthebrightest image i.e. the image of the dot D.

In all respects otherthan those described herein, the arrangement may bethe same as that described in the previous application, appended hereto.

PATENTS ACT 1977 DJUBMC/A4721 GB Title: "Automatically and accurately positioning a workpiece" Description of Invention This invention relates to a method and apparatus for automatically and accurately positioning one workpiece in a set position relativeto another. The invention has been particularly devised for use in assembling a glass panel in a receiving opening of a vehicle component during vehicle assembly, although the invention has many other applications.

In assembling a glass panel in a receiving opening of a vehicle component, it will be appreciated thatthe glass panel must be positioned very accuratelywithin very narrow tolerances to achieve a seal between a glass panel and the receiving opening, andto avoid damagetothe glass panel.

It is established practice for a workpiece such as a glass panel to be positioned by a gripper mounted on a robot arm, underthe control of a computer. The gripper/robot arm is usually articulated such that the workpiece is movable about at leasttwo axes transverse relative to one another. The gripper may thus undergo a compound movementfrom a first position, for example from where the gripperengagesthe workpiece to be moved, to a second set position e.g.

adjacent the other workpiece. Conventionally this compound movement is achieved by using stepper or indexing motors each of which are operable to move the workpiece a defined number of steps and/or servomotorswhich are operable to move the work piece a defined amount, in each case to articulate the parts ofthe robot arm and gripper relative to one another. The computer memory enables the gripperto perform the compound movement repeatedly, by arrangingforthevariousstepperorindexing motors to be stepped or indexed, and/or the servomotors to be actuated in a given orderorsimutaneously.

Howeveraccuratelythe "movable" workpiece is moved by the robot arm, in a fully automated system it cannot be guaranteedthatthe "another" orsecond workpiece is always in an exact position relative to the robotarm.Thusthe movable, first workpiece may be brought to a position which previously was accurately adjacent the previous second workpiece, but because the next second workpiece is in a slightly different position, the first movable workpiece is out of alignment with the second workpiece.

Thus a feedback arrangement is required, such as a sensor to sense the position of the second workpiece usually, relative to the firstworkpiece or robot arm.

Thusthefirstworkpiece may be brought to a position accurately adjacent the second workpiece.

Such a sensor arrangement conventionally comprises a pair of laser or other light sources, a pairof cameras such as television cameras so that the second workpiece can be viewed binocularly, means being provided to analyse the video signals produced by the cameras, to determine the position of the second workpiece relative to the firstworkpiece. The electronic analysing means commonly comprises part ofacomputerwhich is programmed to control the robot.

Although the computer can be programmed to move the gripper and hence the firstworkpiece in response to the feedback arrangement, a further problem ensues due to the mechanical construction of the robot arm. This is that the robot arm may not always be in the exact position to which the computer calculates it has been moved. This discrepancy is due to for example, inertia or backlash i.e. the motors whichoperatetherobotarm arearrangedtoactasa braking means by being operated in reverse directions at the end of travel of the respective robot arm parts, to ensure that movement between anytwo parts is arrested quickly.Inefficiency ofthis braking means can allowthe parts to move relative to one another when such relative movement is not required, for example at the end of relative movement.

Further, where drive to the parts of the robot arm is achieved, by for example, a clutch and/orfexible transmission, inaccuracies in positioning ofthe robot arm parts relative to one another can ensure. Further, wear in the robot arm parts can lead to inaccuracies.

Accordingly it is an object of the present invention to provide a new or improved method and apparatus for overcoming or reducing this problem.

According to one aspect ofthe present invention we provide a method of automatically and accurately positioning a firstworkpiece in a set position relative to a second workpiece comprising the steps of engaging a tool with a first workpiece, moving the first workpiece and tool to a datum position, receiving light from the second workpiece and the tool in an electronic camera, electronically analysing the signal produced by the electronic camera to accurately determine the position or relative position of both the second workpiece and the tool moving the first workpiece to the set position.

Thus any inaccuracies in the movement of the tool and hence first by the robot workpiece can be monitored.

The electronic analysing means may provide information to a control means which causes the first workpiece to be moved to the set position.

Preferablythe information provided takes into account any discrepancy between the actual datum position of the tool and the datum position to which the robot has been prog ram med to move the tool, although if desired, the electronic analysing means may simply provide a warning thatthe robot is not performing as intended, at least when the discrepancy is below a threshold limit.

Preferably, the tool comprises a carrier such as a gripperwhich carries the firstworkpiece, although the tool could compriseanyothertool. Forexample,the first workpiece could comprise a substance which is applied to the second workpiece by an applicator tool.

Preferably, the electronic camera receives light from the second workpiece and the tool simultaneously.

Movement ofthe firstworkpiece and tool is preferably achieved underthe control of a programmable computer, andthe signalfrom the electronic camera maybe analysed by electronic processing means which may be within the computer, so that the computer responds to the signal by moving the carrier or other tool, and hence the firstworkpiece from the datum position to the set position, which may be adjacent or nearer adjacent the second workpiece.

Where the tool comprises a carrier, movement of the carrier and the firstworkpiece from the position in which they are engaged to the datum position may comprise a compound movement about at least two axes transverse relative to one another.

The method may include the step of directing light onto the second workpiece and the carrier or other tool from a light source whereby the light received by the electronic camera is light reflected from the second workpiece and the tool. Alternatively, at least thetool may have a light source such as an array of light emitting diodes which directs lighttothe electronic camera, and light may be reflected or transmitted from the second workpieceto the electronic camera.

Preferably the electronic camera also receives light from the first workpiece in orderthatthe position of the first workpiece relative to the second wo rkpiece can be established.Thusthe method may include the step of determining the position ofthe first workpiece relative to the second workpiece.

In one embodiment, light is received bythe electronic camera, from the first workpiece when the first workpiece is at the datum position, for example simultaneously with the light received from the second workpiece and the tool.

Alternatively a further electronic camera may receive light from the tool and the first workpiece, for example at a position where they are engaged so that the position of the firstworkpiece relative to the tool may be accurately determined priorto moving the tool and firstworkpieceto the datum position.

It will be appreciated thatthroughoutthis specifica tion, by "light" we mean any electromagnetic wave, whethervisible ornotto the eye, although of course the electronic camera needs to be sensitive to the wavelength ofthe light which is used. Conveniently, the light has a wavelength anywhere in the spectrum between and including infrared and ultraviolet light.

Preferably the tool has at least one marking and the electornic means which analyses the signal from the electronic camera atthe datum position, is arranged to recognise the marking to determine the position of the tool, relative to the electronic camera, when the tool and firstworkpiece are in the datum position.

Where light is reflected from the tool to the electronic camera, the marking may comprise one or more dots or holes or other areas of different reflectivityto the background, for example, an array of dots or holes.

Alternatively, where light is transmitted from the tool, the marking may comprise an array of light emitters, such as light emitting diodes.

The second workpieceand/orthefirstworkpiece where light is received from thefirstworkpiece, may have a discontinuity such as an edge or step, onto which the light may be directed and from which the light is reflected to the electronic camera. The electronic camera may be arranged to produce a signal containing a portion which indicates the discontinuity, which portion is recognised bythe electronic analysing means to accurately determine the position or relative position of the second workpiece and/orthefirstworkpiecewhere appropriate.

For example, the electronic camera may comprise a conventional Vidicon tube, or an array of charge coupled devices, or any other camera which is sensitivetothewavelength of light being used, to produce a signal which can be analysed by the electronic analysing means.

Preferably,the method includes the step of arresting the movement ofthetool and hence first workpiece atthe datum position at least sufficiently long enough forthe electronic camera to produce an appropriate signal andlorthe computer or other electronic analysing meansto analyse the signal to accurately determine the position or relative position ofthe second workpiece and the tool and the first workpiece, where appropriate, when in the datum position. Obviously,thefasterthe response time of the electronic camera and the electronic analysing means, the brieferthe firstworkpiece and tool need to be arrested. Possiblythe tool and firstworkpiece may continueto move through the datum position whilst the positions of the tool and first workpiece are being determined.

The method may be applied to avehicle assembly plant Thefirstworkpiece may comprise a panel, such as a glass panel, and the second workpiece may comprise a body part which may have an aperture to receive the panel.

The body part may have a step or recess around the aperture in which the glass panel isto befitted,the step providing a discontinuity which is indicated in the signal produced bythe electronic camera.

Where for example the aperture is generally rectangular, orat Ieasthastwo sides, light maybe received from more than one side of the aperture in each of a respective number of electronic cameras each camera producing a signal, which signals are all analysed by the electronic analysing means.

Thus the position ofthe second workpiece may be more accurately determined in three dimensions than with conventional binoculararrangements.

Where the method is applied to a vehicle assembly plant, the method may include the step of providing sealant to the first workpiece priorto moving the first workpiece to the datum position.

According to a second aspect ofthe invention we provide an apparatus for automatically and accurately positioning a first workpiece in a set position relative to a second workpiece comprising a robot having a tool to engage a firstworkpiece and to move the first workpieceto a datum position, an electronic camera to receive lightfrom the second workpiece and the tool, electronic analysing means to analyse the signal produced by the electornic camera to determine the positions or relative positions ofthe second workpiece and tool, control means to move the first workpiece from the datum position to the set position along a path determined according to the position of the second workpiece previously determined.

The control means may comprise a programmable computer. The electronic analysing means may comprise means ofthe computer or a separate means.

The robotmaycomprise means to enable the tool to be articulated about at least two axes transverse to one another.

The apparatus may include meansto arrest move ment ofthefirstworkpiece and tool at the datum position.

The apparatus may include means to direct light onto the second workpiece and the tool when the first workpiece and the tool are in the datum position, wherebythe light received by the electronic camera is reflected light. The light source maycomprisea laser light source, and means may be provided to cause the laser beam to diverge to provide a fanned beam.

The tool may comprise a carrier such as a gripper suitable for engaging a panel such as a glass panel.

For example, the gripper may have meansto create a vacuum in the gripper whereby the panel is held in engagement with the gripper by means of the vacuum.

The tool may carry a calibration block having a marking such as an array of dots or holes of different reflectivity to the background, or an array of light emitters such as light emitting diodes.

In each case the marking as seen by the electronic camera may indicate to the electronic analysing means, the position or relative position of the tool.

The robot may be provided at a work station of a vehicle assembly plant in which case the first and second workpieces may comprise components of a vehicle.

The second workpiece may be moved tothework station and be stationary at the work stationwhilstthe first workpiece is positioned relative to the second workpiece.

The apparatus in accordance with the second aspect of the invention may have any of the features of the apparatus described which is operated bythe method according to the first aspect of the invention.

The invention will now be described with the aid of the accompanying drawings in which: FIGURE 1 is diagrammatic perspective view of an apparatus for use with the method in accordance with the invention; FIGURE 2 is a diagrammatic plan view of a part of a second workpiece shown at Figure 1; FIGURE 3 is fragmentry sectional view of the workpiece of Figure 2; and FIGURE 4 is diagrammatic illustration of a gauge for use with the apparatus of Figure 1.

Referring firstto Figure 1 there is shown part of an assembly line 10forcars,the part 10 comprising an overhead track. As shown, a car component, in the presentexamplebackpanel 11 of a car body, is transported to a work station at which a robot 12 is situated. The robot 12 is programmed to position a firstworkpiece comprising a glass panel 13 in an opening 14 in the component 11, component 11 comprising a second workpiece.

The robot 12 comprises a fixed base 15 to which is fixed a drive assembly 16, the drive assembly comprising an indexing or stepper motor arranged to rotate a robot body 17 about a first generally vertical axis1.

The robot body 17 is provided with a second drive assembly 18 also comprising an indexing or stepper motor, to rotate a body part 19 about a second generally horizontal axis A2. The body part 19 carries a third drive assembly 20 comprising an indexing motor relative to which another body part 21 slides.

The body pa rt 21 mounts a carrier 22 comprising a gripperofthevacuumtype, to which air lines 24 are connected.

The air lines 24 are used to create a partial vacuum in the gripper 22 sothattheglass panel 13 can be gripped by suction.

Thusthegripper22 and hence panel 13canbe articulated about two pivot axis A1, A2 which are transverse to one another, and can be moved along a third axisA3 bythe motors ofthe drive assemblies 16, 18and20.

The motors are controlled by a remote programmable computer 25, the control line being indicated at 26. Further, an air pump (notshown) which causesthe vacuum in the gripper 22 and lines 24, is controlled by the computer 25 sothatthe glass 13 can be engaged and disengaged underthe control ofthe computer 25.

To detect the exact position ofthe second workpiece i.e. the car component 11 relative to the robot 12, a gauge 30 is provided,the gauge being fixed relative to the base 15 of the robot 12. The gauge 30 may be mounted adjacent to the robot 12 as shown, or could be mounted overhead, or on the robot 12, or in any otherfixed position relative to the robot 12, where the gauge 30 can sense the position of partofthefirstand second workpieces 13, 11 as hereinafter described.

In the example described,fourgauges 30 are provided to view different parts ofthe workpieces 13, 11, although only one gauge is shown for clarity.

The gauge 30 itself will be described in more detail hereinafterwith reference to Figure 4.

The gauge directs a fan 31 of laser lighttowardsthe opening 1 4 of the component 11. Some ofthis light is reflected and is received by an electronic camera within the gauge 30. The camera produces a video signal which may be displayed as a picture on a monitor screen if desired, as shown at 33, which signal is electronically analysed by electronic analysing means ofthe computer 25.

The opening 14 in the component 11 has a periphery of stepped configuration as can be seen from Figures 2 and 3, a step 34 being provided in which the periphery of the glass panel 13 is received, as indicated in dotted lines in Figure 3. Adhesive or other sealant is applied to the periphery of the panel 13 prior to panel 13 being assembled in the opening 14 at an upstream work station, so that when the periphery of the glass panel 13 is received in the step 34, a seal is achieved between the panel 13 and the step 34. If desired, a trim strip may subsequently be applied to conceal the joint between the glass panel 13 and the component 11.

Thefan 31 of laser light31 has an axis Fwhich is generallytransverseto one side 35 of the opening 14 onto which thefan 31 is directed.

The axis Fofthefanof light31 is in the present example, at about30 to the side 35. Thus the image of the reflected lightwill appear as indicated on the monitor33 in Figure 1.

Thecomputer25 is programmed to convert the signal produced by the electronic camera of the gauge 30 a portion of which indicates the step 34, into a digital form and to use this information to detect the exact position of the component 11.

The opening 14 hasthree othersides 36,37 and 38 and is of generally rectangularconfiguration. As said above, four gauges are provided in this example, two of the otherthree gauges sensing the position of the side 36, and the other gauge sensing the position of the side 37.

Using the information from all four gauges, the computer 25 can accurately determine the position of the component 11 and hence the opening 14, in three dimensions. This contrasts with known arrangements which rely on binocularvision i:e. two gauges examine a common partofacomponenttodetermine the position ofthe component.

The gripper 22 carries four calibration blocks 23 each of which lies within the field of view of one ofthe gauges, when the firstworkpiece 13 is in a datum position shown, to which position the computer 25 instructsthe robot 12to move the gripper 22 and hence the glass panel 13 prior to assembling the glass panel 13 in the opening 14.

To illustratethis an image 23' of the calibration block 23 corresponding to gauge30, is shown on screen 33.

To monitorwhetherthe gripper 22 and hence panel 13 is in the position to which the computer has instructed the robot 12 to move the gripper each calibration block 23 is provided with a marking which is seen bythe camera of the gauge 30. In the present example, the marking comprises an arrayoffive dots or holes 24 or different reflectivity to the remainder of the block 23, but alternatively the marking could be an array of light emitters such as light emitting diodes which transmit lightto the camera of the gauge 30.

When analysing the signal produced by the camera of the gauge 30 (and also the other gauges), the computer 25 is programmed to recognize that portion of the signal which indicates the marking. Thus the computer25 can check by comparing the signal with programmed data,thatthe gripper 22 and hence panel 13 is in the presumed position.

If desired, the computer 25 may thus make anyfine adjustments required to move the gripper 22 into the exact predetermined datum position, orthe computer may simply take account of any discrepancy between the presumed position of the gripper 22 and its actual position, when moving the gripper 22 and hence the glass panel 13 from the datum position to bring the panel 13 into engagement with the step 34 ofthe opening 1 4 of the component 11.

However, in the example described the computer 25 merely provides an indication to an operatorthatthe robot 12 is not performing accurately, at least until the degree of inaccuracy reaches a predetermined threshold, when the computer may be arranged shutdown the robot 12 until repairs are undertaken.

It will be appreciated that in orderthatthe panel 12 can be accurately placed in opening 14, it is also necessary to establish exactly the position ofthe panel 13 atthe datum position. This can be done by providing a position sensing apparatuswherethe gripper 22 engagesthe panel 13. By moving the gripper 22 along a predetermined path to the datum position, the position of panel 13 can thus be known.

Preferably though, the position of panel 13 is sensed atthe datum position. To achieve this it can be seen that each ofthe calibration blocks 23 has a cut out 26 through which the adjacent edge 27 ofthe panel 13 can be seen. The periphery of the panel 13 had an edge strip of material 28 (see figure 3) which thus provides a discontinuity, which like step 34 of opening 14 gives rise to an image which is illustrated at 27' on screen 33.

Again the computer is programmed to recognise that portion ofthe video signal produced bythe camera ofthe gauge 30, and also the other gauges, to accurately determine the position of panel 13 relative to the robot 12.

Thus movement of the panel 13 from the datum position shown, to the-set position in aperture 14 can be achieved because the relative positions of component 11 and component 13 can be determined. Further becausethe calibration blocks 23 can be viewed, the performanceofthe robot 12 in moving the panel 13to the datum position, can be monitored.

Operation ofthe system will now be described.

The gripper 22 of the robot 12 is articulated by the robot 12to a loading station atwhich glass panel 13 is engaged bythe gripper. Avacuum isformed inthe gripper 22, and thus the panel 13 becomes fixed relative to the gripper 22 by suction.

If desired, this operation may be "seen" by a position sensing means.

The robot 12 is then articulated in a predetermined sequence of movements, to bring the gripper 22 and hence panel 13 to the datum position shown in Figure 1 which is sufficiently close to component 11 forthe component 11 as well as the edge 27 of panel 13 and the calibration blocks 23 to give sharp images for the cameras ofthe gauges. This may involve actuation of the drive assembly 16 and/or drive assembly 18 and/or drive assembly 20. In the datum position, motion of the gripper 22 is arrested whilst a signal is produced bythe camera of gauge 30, and the cameras of the other gauges.

The time for which motion ofthe robot 12 is arrested will depend upon the response time ofthe apparatus.

The computer 25 will thus determine not only the exact relative positions ofthe components 11 and 13, but the exact position of the calibration blocks 23 relative to the robot base 15. The computer 25 can then determine the exact movement required to bring the glass panel 13 into alignment and engagementwith the step 34 of the opening 14 of the component 11 and the performance ofthe robot 12 can be monitored.

The system described has of course many uses in addition to positioning glass panels in openings in automobile components.

For example instead of a gripper22 provided on the robot arm 14 being ofthe vacuum type an alternative type ofgripperorcarriercould be provided to grip/carryanyotherworkpiece may be provided.

Alternatively, anothertool such asameansfor applying thesealanttothe glass panel 13 maybe provided on a robot, at a work station upstream ofthe workstation shown in Figure 1 which other work station may be operated bythe method described. In this event the meansfor applying the sealant may have a marking so that gauges such as gauge 30 can accurately monitorthe performance of that robot.

Further, the system and method may be applied to any other application where it is desired to position one workpiece in engagement or adjacent relative to another workpiece automatically and accurately.

Of course, although as described, a robot 12 which permits movement of a workpiece gripped by a gripper about two transverse axes Al ,A2 and along a third axis A3 has been described, any other robot may be used in the system described, to move one workpiece to a position in engagement or adjacent anotherworkpiece. For example, a six axis robot may be employed.

Referring now to Figure 4the construction of gauge 30 will now be described.

The gauge 30 comprises a laser light source 50 which produces a beam of laser light 51. The beam is reflected by an optically flat mirror 52 and is then passed through a cylindrical lens 53. This causes the beam to diverge i.e. become fanned out slightly in a direction ofthe plane ofthe paper ofthe drawings. The fanned beam 31 is then emitted from a casing 57 of the gauge 30through an outlet aperture 58 and is directed to a workpiece 11 as described hereinbefore. Light is reflectedfromtheworkpiece 11 as seen along beam path 54 and is received by a suitably positioned electronic camera 55 such a video, television camera or a camera comprising an array of charge coupled devices. It can be seen that the camera 55 is placed at an angle of approximately 30" the workpiece as it has been found that this angle gives the best signal definition of any discontinuity ofthe workpiece such as a step 34. However the camera could be placed at other angles if desired.

The width Wofthe gauge 30 is significantly reduced compa red with known gauges of this type, because the laser 50 which necessarily has to be long, is arranged transverse relative to the direction along which the beam 31 is emitted. This is achieved by virtue of the mirror 52 which is placed in the path ofthe beam 51 of laser light. This reduction of width W ofthe gauge is an important advantage where there is a restriction in space on which the gauge 30 can be mounted.

In use, the laser 50 is operated continuously to preserve its useful working life, but the gauge 30 is operated only intermittently, when the movable workpiece i.e. glass panel 13 is in the datum position, for safety reasons. To achieve this a shutter 56 is provided so that the laser light emitted from the casing 57 can be switched on and offsubstantially instantaneously. Thus the exposure time to the laser beam 31 at the workstation is minimised. Movement oftheshutter56 into and outofthe path of laser light is preferably achieved underthe control of the computer 25. The shutter 56 is preferably resiliently biased by mechanical urging means to a closed position, in the path of beam 51.Thus the sh utter 56 has to be moved out of the path of beam 51 by power means to enable the light to be emitted from casing 57. This provides a fail safe arrangement in that in the event of power failure, the lightwill not be emitted.

As shown,the laser 50 and camera 55 are closeto one another because the separation of beam 31 and camera 55 does not need to be large. For example where the distance between the camera 30 and the workpiece 11 is small it has been found that the maximum length L of the gauge 30 for a distance from gauge 30 to workpiece 11 of 12 inches (30.48cm), need only be 22 inches (55.88 cm), increasing to 30 inches (76.2cm) where the distance from gauge 30 to workpiece 11 is increased to 24 inches (60.96 cm).

Where the distance between gauge 30 and work- piece 11 is increased to 36 inches (91.44 cm), the gauge 30 would need to have a length of about 36 inches (91.44cm) to enable there to be sufficient separation between the emitted beam 31 and the camera 55.

In another arrangement the lens 53 may be omitted and instead of a fan 31 of light, a cross may be generated, or any other light form provided that the camera 55 can distinguish the discontinuity on which the light impinges, to provide an electrical signal to computer 25 which can be analysed.

The features disclosed in the foregoing description, orthe following claims, orthe accompanying drawings, expressed in their specific forms or in terms of a means for performing the disclosed function, or a method or process for attaining the disclosed result, ora class or group of substances or compositions, as appropriate, may, separately or in any combination of such features, be utilised for realising the invention in diverse forms thereof.

Claims (48)

1. A method of automatically and accurately positioning a firstworkpiece in a set position relative to a second workpiece comprising the steps of engaging a tool with the firstworkpiece, moving the firstworkpiece andtoolto a datum position, receiving light from the second workpiece and the tool in an electronic camera, electronically analysing the signal produced by the electronic camera to accurately determine the position or relative position of both the second workpiece and the tool, and moving the first workpiece to the set position.

2. A method according to Claim 1 wherein the tool is carried by a robot which moves the tool to the datum position to move the firstworkpiece to the set position.

3. A method according to Claim 2 wherein the electronic analysing means provides information to a control means which controls the robot to cause the firstworkpiece to be moved to the set position.

4. A method according to Claim 3 wherein the information provided takes into account any discrepancy between the actual datum position of the tool and the datum position to which the robot has been programmed to movethetool.

5. A method according to Claim 2 wherein the electronic analysing means provides a warning that the robot is not performing as intended, when any discrepancy between the actual datum position ofthe tool and the datum position to which the robot has been programmedtomovethetool,isbelowa threshold limit.

6. A method according to any one ofthe preceding claims wherein the tool comprises a carrier which carries the first workpiece.

7. A method according to any one of Claims 1 to 5 wherein thefirstworkpiece comprises a substance which is applied to the second workpiece by an applicatortool.

8. Amethod according to anyone ofthe preceding claims wherein the electronic camera receives light from the second workpiece and the tool simultaneously.

9. A method according to any one of the preceding claims wherein movement of the first workpiece and tool is achieved underthe control of a programmable computer.

10. A method according to Claim 9 wherein the signal from the electronic camera is analysed by electronic processing means within the computer, so that the computer responds to the signal by moving the tool, and hence the firstworkpiece from the datum position to the set position, which may be adjacent or neareradjacentthe second workpiece.

11. A method according to any one of Claims 6to 10 where appendantto Claim 6 wherein movement of the carrier and the firstworkpiece from the position in which they are engaged to the datum position comprises a compound movement about at least two axes transverse relative to one another.

12. A method according to any one of the preceding claims which includes the step of directing light onto the second workpiece and the tool from a light source.

13. A method according to any one of Claims 1 to 11 wherein at least the tool has a light source which directslighttotheelectroniccamera, light being reflected ortransmitted from the second workpiece to the electronic camera.

14. A method according to any one ofthe preceding claims wherein the electronic camera also receives light from thefirstworkpieceto determine the position ofthe first workpiece relative to the second workpiece.

15. A method according to Claim 14wherein light is received bythe electronic camera, from the first workpiece when the firstworkpiece is atthe datum position simultaneously with the light received from the second workpiece and thetool.

16. A method according to Claim 1 4wherein a further electronic camera receives light from the tool and thefirstworkpiece, at a position where they are engaged sothatthe position ofthefirstworkpiece relative to thetool may be accurately determined prior to moving the tool and firstworkpiece to the datum position.

17. A method according to any one of the preceding claims wherein the tool has at least one marking and the electronic means which analyses the signal from the electronic camera atthe datum position, is arranged to recognisethe marking to determine the position of the tool, relative to the electronic camera, when the tool and firstworkpiece are in the datum position.

18. A method according to Claim 17 where appen- dantto Claim 12 whereinthe marking comprises one or more areas of different reflectivity to the background.

19. A method according to Claim 17whereappendantto Claim 13 wherein the marking comprising an array of light emitters.

20. A method according to any one ofthe preceding claims wherein the second workpiece andlorthe firstworkpiece where light is received from the first workpiece, has a discontinuity onto which the light may be directed and from which the light is reflected to the electronic camera.

21. A method according to Claim 20 wherein the electronic camera is arranged to produce a signal containing a portion which indicates the discontinuity, which portion is recognised bythe electronic analyse ing meansto accuratelydeterminethe position or relative position of the second workpiece and/orthe firstworkpiece.

22. A method according to any one ofthe preceding claimswhereinthe electronic camera comprises a Vidicon tube, or an array of charge coupled devices, to produce an electronic signal which can be analysed by the electronic analysing means.

23. A method according to any one of the preceding claims wherein the method includes the step of arresting the movement ofthetool and hence first workpiece at the datum position at least sufficiently long enough forthe electronic camera to produce an appropriate signal andlorthe computer or other electronic analysing means to analyse the signal to accurately determine the position or relative position of the second workpiece and the tool, and the first workpiece where appropriate, when in the datum position.

24. A method according to any one of Claims 1 to 23 wherein thefirst workpiece comprises a panel, and the second workpiece comprises a body part which has an aperture to receivethe panel.

25. A method according to Claim 24 wherein the body part has a step or recess around the aperture in which the panel isto befitted, the step providing a discontinuity which is indicated in the signal produced bythe electronic camera.

26. A method according to Claim 24 or Claim 25 when the aperture has at least two sides, and light is received from more than one side of the aperture in each of a respective numberofelectronic cameras each camera producing a signal, which signals are all analysed by the electronic analysing meansto deter mine the position of the second workpiece in three dimensions.

27. A method according to any one of Claims 24to 26 wherein the method includes the step of providing sealantto the first workpiece priorto moving the first workpiece to the datum position.

28. A method of positioning a workpiece substantially as hereinbefore described with reference to the accompanying drawings.

29. An apparatus for automatically and accurately positioning-a firstworkpiece in a set position relative to a second workpiece comprising a robot having a tool to engage a firstworkpiece and to movethefirst workpiece to a datum position, an electronic camera to receive lightfrom the second workpiece and the tool, electronic analysing means to analyse the signal produced bythe electronic camera to determine the positions or relative positions of the second workpiece and tool, control means to move the first workpiece from the datum position to the set position along a path determined according to the position of the second workpiece previously determined.

30. An apparatus according to Claim 29 wherein the control means comprises a programmable computter

31. An apparatus according to Claim 29 or Claim 30 wherein the robot comprises meanstoenablethe tool to be articulated about at least two axes transverse to one another.

32. An apparatus according to any one of Claims 29to 31 which includes meansto arrest movement of the firstworkpiece and tool atthe datum position.

33. An apparatus according to any one of Claims 29 to 32 which apparatus includes means to direct light onto the second workpiece and the tool when the firstworkpiece and the tool are in the datum position, wherebythelightreceived bythe electronic camera is reflected light.

34. An apparatus according to Claim 33wherein the light source comprises a laser light source, and means are provided to cause the laser beam to diverge to provide a fanned beam.

35. An apparatus according to any one of Claims 29 to 34 wherein the tool comprises a carrier suitable for engaging a panel the carrier having meansto create a vacuum whereby the panel is held in engagement with the carrier by means of the vacuum.

36. An apparatus according to any one of Claims 29 to 35 wherein the tool is a calibration block having markings of different reflectivitytothe background, or an array of light emitters.

37. An apparatus according to any one of Claims 29 to 36 which comprises part of a work station of a vehicle assembly plant, the first and second workpieces comprising components of a vehicle.

38. An apparatus according to any one of Claims 29 to 37 wherein the electronic camera also receives light indicating the position ofthe firstworkpiece so that the relative position ofthe firstworkpiece, the tool, and the second workpiece can be determined.

39. An apparatus according to Claim 38 wherein a screen is positioned between the first workpiece and the electronic camera to receive light reflected from an edge ofthefirstworkpiece and provide an enhanced imageforthe electronic camera.

40. An apparatus according to Claim 39 wherein the screen is placed between the first workpiece and the camera a known distance from thefirstworkpiece.

41. An apparatus according to Claim 40 wherein the screen is carried bythetool.

42. An apparatus according to Claim 41 wherein the tool has means to move the screen into position subsequenttothetool engaging with thefirst workpiece so that the screen does not interfere with the normal operation ofthe tool.

43. An apparatus according to Claim 38 wherein a screen is positioned such that the first workpiece is between the screen and the electronic camera, light which passes the first workpiece being received on the screen to provide a shadow image ofthe first workpiece which is viewed by the electronic camera.

44. An apparatus according to Claim 43 wherein the screen is spaced a known distance from the first workpiece, and is carried by the tool.

45. An apparatus according to Claim 44wherein the tool moves the screen into position subsequent to the tool engaging the first workpiece.

46. An apparatus according to Claim 38 wherein the electronic camera is provided with a low band filter so that only the brightest image of the firstworkpiece is seen bythe camera.

47. An apparatus substantially as hereinbefore described with reference to and as shown in the accompanying drawings.

48. Any novel feature or novel combination of features as herein defined and/or shown in the accompanying drawings.