GB1586464A - Automatic positioning - Google Patents

Description

(54) AUTOMATIC POSITIONING (71) We, BOC Limited, an English Company, of Hammersmith House, London, W6 9DX, England, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This present invention relates to apparatus for monitoring and regulating automatically the position of a heat source relative to a surface of a workpiece.

In United Kingdom patent No. 1559833 there is described a process and apparatus for enabling an automatic welding machine to follow a seam to be welded with sufficient precision to eliminate the need for an operator to guide the movement of the welding torch relative to the workpiece.

In United Kingdom patent No. 1559833, tubular workpieces to be welded are mounted on a workholder having driven support and positioning rollers which are able to rotate the workpieces about their common axis. In operation. the motors controlling the rollers are energised to cause the workpieces to rotate at a speed appropriate to the welding process so that the weld seam between the workpieces transverses past a welding torch which is substantially stationary.

In use, the welding torch is generally held above the top dead-centre of the weld seam, or at a location along the weld seam slightly below top dead-centre. in a disposition such that the welding head of the torch is normal to the surface of the workpieces. When making a weld. it is desirable that. as the workpieces rotate. the torch should remain at the same chosen location relative to the moving surface of the workpiece. that in, at top dead-centre of the weld seam, or slightly below. However. most tubular workpieces are not trulv circular. so that, as the workpieces rotate, the top dead-centre of the weld seam (or a point on the weld seam slightly below top dead-centre) will move in a curved line or a closed loop in a vertical plane through the seam to be welded.

According to the present invention, a combined line follower and height sensor apparatus for monitoring and regulating automatically the position of heat source relative to a surface of a workpiece includes a height sensor which comprises a source of radiation so positioned, that when in use, it directs a beam of radiation along a first predetermined path onto a reflective surface on the workpiece, the reflective surface reflecting the beam along a second predetermined path towards a radiation sensitive means, the radiation sensitive means generating a signal responsive to any deviation of the beam of radiation from the second predetermined path and at least one motor actuable by the signal from the radiation sensitive means for regulating the position of the heat source relative to the surface of the workpiece.

Preferably the heat source is an electric arc welding torch, such as a MIG, TIG or plasma torch. and the workpiece is a metal plate, pipe or other assembly to be welded.

In a preferred embodiment of the apparatus, the sensing means takes the form of an array of photo-electric cells, suitably four such cells arranged at the apices of a square, positioned transversely to the reflected beam. Generally, the centre of the array would be positioned so that it intercepts the reflected beam when the welding torch is placed at the chosen height above the surface of the workpiece.

For most applications. the welding torch and the radiation source and its associated sensing means are all mounted on the same support, the movement of which is controlled to correct for changes both in the height of the welding torch above the workpiece and in the location of the welding torch relative to the path of the weld seam.

It is envisaged that for some very accurate applications it might be necessary for the welding torch on the one hand, and the radiation source and sensing means on the other, to be mounted on separate supports so that they can move independently. In such case there will have to be a time delay from the time when the sensing means records a deviation of the reflected beam to the time when the position of the welding torch is corrected by the said motor.

Accordingly, for such very accurate applications, the apparatus desirably includes a time delay or other memory svstem which will enable the position of the welding torch to be corrected at a chosen time after the sensing means has recorded the deviation of the reflected beam.

Preferably, the reflected surface used in conjunction with the apparatus of the present invention takes the form of an adhesive tape having an outer reflective surface, which tape is secured to the surface of the workpiece running alongside. preferably parallel to, the seam to be welded.

An embodiment of the invention will now be described by way of example. reference being made to the Figures of the accompanying diagrammatic drawings. in which: Figure I is a schematic front view of an apparatus for monitoring and regulating the position of a heat source relative to a surface of a workpiece.

Figure 2 is a schematic side view of the apparatus of Figure 1; Figure 3 is a schematic front view of the array of photo-electric cells forming part of the apparatus of Figure 1: and Figure 4 is a diagram showing the geometric relationship between some of the components of the apparatus of Figure 1.

The apparatus as shown in Figures 1 and 2 include a heat source in the form of an electric arc welding torch 2 depending from a platform 4. The torch 2 is movably mounted so that it can be selectivelv moved along the platform parallel to the weld seam 6 thereby to varv the distance x (see Figure 2) between it and a source of radiation in the form of a light source 10. The platform is held above two tubular workpieces X bv support means (not shown). Suitable support means are described in United Kingdom patent No. 1559833.

I he light course 10 and radiation sensitive means in the form of a light sensor 12 also depend from the platform 4. The light source 10 and sensor 12 are mounted so as to pivot contiollablv about axes 14 and 16 respectively. In addition the sensor 12 can be moved along a slot 34 in a support strut 20 to enable the angle H shown in Figure 2 to be varied.

In operation. the various components of the apparatus will require supplies of various services, inter alia, electrical energy, welding consumable, shielding gas, but these have not been shown in the drawings as it will be evident to those skilled in the art what services are necessary for operation of these components.

The workpieces 8 are mounted on a workholder (not shown) having driven rollers which are able to rotate the workpieces about their common axis. In operation, the motors controlling the rollers are energised to cause the workpieces to rotate at a speed such that the seam 6 to be welded travels past the welding torch 2 at a speed appropriate for the welding process.

The welding torch 2 is arranged to follow automatically the seam to be welded by incorporation in the apparatus of a linefollowing system as described in United Kingdom patent No. 1559833.

A tape 11, preferably self-adhesive. is secured to the outer surface of one of the workpieces 8 so as to run substantially parallel to the seam to be welded. The outer surface of the tape l l is coated with a layer of reflective material.

The light sensor 12 includes an array of four photoelectric cells 18 (shown in Figure 3) for detecting light reflected from the reflective tape 11. In operation. the height d of the platform 4 above the workpiece surfaces is set so that the welding torch 2 is at a desired height about the seam to be welded. The orientations of lamp 10 and light sensor 12 about axes 14 and 16 respectively are adjusted so that. when the platform 4 is at the said distance d. the light beam 22 from the lamp 10 impinges upon the reflective surface of tape 11 and is reflected to the centre 24 of the array of photoelectric cells 18. each cell therefore receiving an equal amount of radiation.

To make a weld. the tubular workpieces 8 are rotated slowlv and the electric arc welding torch 2 is energised. thereby to deposit weld metal in the seam between the two workpieces. If. owing to a decrease in the effective diameter of the tubular workpiece. the height d of the platform 4 above the surface of the workpieces 8 should increase at any time. the reflected beam 26 will move downwardly (as viewed: direction a in Figure 3) -. relatively to the array of cells 18: the lover two cells 18 will thus receive more radiation than the upper two cells 18. The cells 18 will produce signals indicating the amount of deviation ofthe path reflected beam 26 from its predetermined path to the centre of the array of cells. These signals are conveved lfia electrical conductors 28 to a control unit 30 which operates motors 32. bv means of which the platform 4 can be returned to the chosen height d above the workpieces 8.

Conversely, if the height d should decrease, owing to an increase in the effective diameter of the tubular workpiece, the reflected beam 26 will move upwardly (as viewed; direction b in Figure 3) relatively to the array of photocells 18; in this case the upper two cells will receive more radiation than the lower cells. As before, the signals generated by the cells are fed to the control unit 30 which then activates motors 32 to return platform 4 to its chosen height d above the workpiece. The control unit 30 incorporates a servo-mechanism which controls motor 32 to adjust the height of platform 4 above the workpieces 8 until the reflected beam 26 follows its predetermined path to the centre 24 of the array of photocells.

In order to maintain the welding head of the welding torch 2 at the top dead-centre of the weld seam, or at a similar position along the' weld seam slightly below top deadcentre, the control unit 30 is adapted to respond to the different electrical signals produced when different amounts of radiation fall on the two left-hand and two right-hand (as viewed in Figure 3) photoelectric cells 18. and to actuate driving means 36 to return the torch to its intended position. The different amounts of radiation are caused bv the movement of the reflected beam in directions c orf(as shown in Figure 3) which results from the deflection of the reflected beam out of a plane containing the pre-set paths chosen for the incident beam and reflected beam to follow.

If. for example. it is desired to weld at top dead-centre. the lamp 10 and the sensor 12 can both be positioned in the same nonvertical radial plane relative to the axis of workpieces 8. and oriented about transverse axes 14 and 16 respectivelv so that the incident beam 22 will fall. after reflection at reflective surface 11. at the centre 24 of the arrav of photo-electric cells 18.

As the workpieces rotate. if thev are out-of-round the plane containing the incident beam of light 22 will no longer impinge perpendicularly on the workpiece surface.

Consequently. the reflected beam of light 26 will no longer lie in the radial plane. The reflected beam will therefore be displaced laterallv when it reaches the sensor 12 (in direction c or f as shown in Figure 3) and will cause electric signals of differing magnitudes to be generated by the various photocells in the array. These different signals are fed to control unit 30 which then actuates appropriate motors 32 for moving the platform 4 so that the welding torch 2 is moved in a direction parallel to the seam to be welded until it is at top dead-centre once again.

A similar arrangement can be used if welding is to be performed off top deadcentre, by adjusting the distance of separation (x in Figures 2) of the welding torch 2 from the light source 10 by an appropriate amount so that the welding head of the torch 2 is at the desired location on the weld seam below top dead-centre. In such a case, the light source 10 and sensor 12 could be positioned in a vertical radial plane.

In some instances, it may be preferably to mount the light source 10 so that the incident beam 22 follows a path lying in a vertical plane rather than lying in a radial plane.

If the light source 10 in such an arrangement is at top dead-centre. the incident beam 22 and reflected beam 26 will both lie in a vertical radial plane when the incident beam 22 impinges on the workpieces at top dead-centre. If the workpieces are out-ofround, the top dead-centre of the weld seam will move laterally relative to the incident beam 22 so that the vertial radial plane containing the incident beam no longer extends perpendicularly to the workpiece surface. Consequently, the reflected beam 26 no longer is in a vertical radial plane and is deflected laterally relative to the array of photoelectric cells. As described above, suitable corrections to the position of the welding torch can them be made by moving platform 4 in a direction parallel to the weld seam.

A situation where the light source 10 is orientated to direct an incident beam 22 in a vertical plane which is off top dead-centre is illustrated in Figure 4. Here the incident beam 22 is set to impinge on the reflective surface 11 at a point which is p" below top dead-centre. In such a case. at the point of incidence 28 the plane I containing the incident beam 22 and running parallel to the common axis of the workpieces through the point of incidence 28 will be at an angle p" to radial plane C. as will be the plane R which contains reflected beam 26 and which runs parallel to the common axis of the workpieces. In operation. if the incident beam is to impinge on the reflective surface at an angle p" below top dead-centre. the light source 10 and sensing means 12 are adjusted so that the respective planes I and R containing them are inclined one to another at an angle zip". As before the horizontal distance of separation x between the welding torch 2 and light source 10 can then be varied as desired to enable the welding torch to be positioned at top dead-centre of the workpieces or at a position along the weld seam below top dead-centre. If the workpieces are out-of-round. as mentioned be fore the reflected beam '(r w will deviate from its pre-set path and move laterallv in direction c orf(see Figure 3) relative to the array of photocells 18. The resultant electric signals can then be used to make suitable corrections to the position of the welding torch 2 until it is returned to its set position.

Although the apparatus of the present invention has been described in relation to positioning an arc welding torch relative to a seam to be welded; it is clearly applicable to positioning other heat sources such as a laser or a source of high energy relative to the surfae of a workpiece.

WHAT WE CLAIM IS: 1. A combined line-follower and height sensor apparatus for monitoring and regulating automatically the position of a heatsource relative to a surface of the workpiece, the height sensor comprising a source of radiation so positioned, that when in use, it directs a beam of radiation along a first predetermined path onto a reflective surface on the workpiece, the reflective surface reflecting the beam along a second predetermined path towards a radiation sensitive means, the radiation sensitive means generating a signal responsive to any deviation of the beam of radiation from the second predetermined path and at least one motor actuable by the signal from the radiation sensitive means for regulating the position of the heat source relative to the surface of the workpiece.

2. An apparatus as claimed in claim 1, in which the heat source is an electric arc welding torch and the radiation sensitive means is an array of photo-electric cells.

3. An apparatus as claimed in claim 2, in which four photo-electric cells are provided and arranged at the apices of a square positioned transversely to the second predetermined path.

4. An apparatus as claimed in any one of claims 1 to 3, in which the heat source, the source of radiation and the radiation sensitive means are all mounted on the same support, the movement of which support is controlled by the motor.

5. An apparatus as claimed in any one of claims 1 to 3, in which the heat source is mounted on one support whilst the source of radiation and the radiation sensitive means are mounted on a different support, the supports being movable independently.

6. An apparatus as claimed in claim 5, in which a time delay is provided for permitting the regulation of the position of the heat source at a predetermined time after the radiation sensitive means has sensed any deviation of the reflected beam.

7. An apparatus for monitoring and regulating automatically the position of a heat source relative to a surface of a workpiece, constructed and arranged substantially as hereinbefore described, with reference to and as illustrated in the Figures of the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (7)

**WARNING** start of CLMS field may overlap end of DESC **. corrections to the position of the welding torch 2 until it is returned to its set position. Although the apparatus of the present invention has been described in relation to positioning an arc welding torch relative to a seam to be welded; it is clearly applicable to positioning other heat sources such as a laser or a source of high energy relative to the surfae of a workpiece. WHAT WE CLAIM IS:

1. A combined line-follower and height sensor apparatus for monitoring and regulating automatically the position of a heatsource relative to a surface of the workpiece, the height sensor comprising a source of radiation so positioned, that when in use, it directs a beam of radiation along a first predetermined path onto a reflective surface on the workpiece, the reflective surface reflecting the beam along a second predetermined path towards a radiation sensitive means, the radiation sensitive means generating a signal responsive to any deviation of the beam of radiation from the second predetermined path and at least one motor actuable by the signal from the radiation sensitive means for regulating the position of the heat source relative to the surface of the workpiece.

2. An apparatus as claimed in claim 1, in which the heat source is an electric arc welding torch and the radiation sensitive means is an array of photo-electric cells.

3. An apparatus as claimed in claim 2, in which four photo-electric cells are provided and arranged at the apices of a square positioned transversely to the second predetermined path.

4. An apparatus as claimed in any one of claims 1 to 3, in which the heat source, the source of radiation and the radiation sensitive means are all mounted on the same support, the movement of which support is controlled by the motor.

5. An apparatus as claimed in any one of claims 1 to 3, in which the heat source is mounted on one support whilst the source of radiation and the radiation sensitive means are mounted on a different support, the supports being movable independently.

6. An apparatus as claimed in claim 5, in which a time delay is provided for permitting the regulation of the position of the heat source at a predetermined time after the radiation sensitive means has sensed any deviation of the reflected beam.

7. An apparatus for monitoring and regulating automatically the position of a heat source relative to a surface of a workpiece, constructed and arranged substantially as hereinbefore described, with reference to and as illustrated in the Figures of the accompanying drawings.