GB2113142A - Apparatus and method for laser perforation of moving material - Google Patents

Abstract

Irregation tubing 12 has a supply tube 16 and an emitter tube 14 with a common wall 17. The laser 2 is used to perforate the wall of the emitter tube 14 and/or the common wall 17 while the tubing 12 is travelling in direction A. The laser beam 6 reflected by a rotating twelve-sided mirror 8 sweeps across the diameter of the lens 10 and thus its focus 18 is held at the same point along the moving tubing. To perforate the wall 17 the lens can be shifted to the position shown in broken lines or a split lens may be used with half at each position. <IMAGE>

Description

SPECIFICATION Apparatus and method for laser perforation of moving material In the past there has been a desire to perforate thermo-plastic tubing used for irrigation with a laser. Typically, this has been accomplished with a laser using a lens to focus the beam on the material such that a perforation was made at the desired place. However, to accomplish this on material moving at a certain rate of speed in a linear direction, has required expensive and complicated systems.

In recent years there has been a development of irrigation tubing in which there is a supply tube and an emitter tube joined by a common wall. The supply tube supplies water to the emitter tube at a certain rate. The emitter then supplies the proper amount of water for irrigation. In each case the correct rate of flow of water is dictated by the amount and size of the perforations in the wall between the supply and emitter tubes and those perforations in the emitter tube itself.

Those systems used to accomplish such activity as previously stated, tended to be more complex and more expensive because of the thickness of the thermo-plastic tube to be perforated. The system must be able to track the moving tubing such that the laser beam is focussed on the tubing for a sufficient amount of time so that the desired perforation hole size can be realized. Additionally, there has been a mechanical device to either move the laser itself while tracking the tube or a mechanical device, such as a rotating wheel, with a laser beam bending apparatus, to track the beam with the moving tube.

The previous techniques used to accomplish this have only been marginally satisfactory and are rather complex. Much of the difficulty arises around the problem of maintaining the alignment of the tubing while it is being perforated by the laser. If there is slight deviations in the tracking of the laser beam, this causes misalignment while the tube is moving through the lasing area resulting in improperly perforated holes.

Summary of the Invention The present invention overcomes these problems by providing a system and method for using the same to perforate the supply tube and emitter tubes individually or simultaneously.

In accordance with one embodiment of the invention, a laser serves as the source of coherent light with a timer connected thereto. The timer connected to the laser is used to determine the light pulsing interval and the duration of the light pulse. The coherent light is directed to a rotatable reflecting means such as a polysided mirror or reflector which directs the incoming beam to a focussing lens. The focussing lens can be of conventional type, however the most desirable is a lens which provides minimum distortion over maximum field flatness. The optimum design is a telecentric lens system. As the beam of light is reflected by the rotating polysided mirror, the beam sweeps across the diameter of the lens. The system is of a configuration such that the focal point will remain an equal distance from the lens and moves in a plane parallel to the lens during the sweep.When the surface of the moving material is placed in the plane of the focal point, the beam remains incident at the same point on the surface of the moving material during the entire length of the sweep of the beam along the diameter of the lens.

The sweep of the laser beam is at a rate consistent with the movement rate of the tubing so that the focal point of the beam remains in one spot on the tubing. The sweep time is necessary so that the laser beam has enough time to perforate the thermo-plastic material from which the irrigation tube is constructed. The lens is of a sufficient diameter such that the length of time necessary for perforating the thermo-plastic material is accomplished during the sweep of the beam across it.

In another embodiment of the invention, means is provided to move the focussing lens from an original position to a second position to focus the beam at a different position. When it is desired to perforate only emitter tube, the lens is positioned as previously described. When it is desired to perforate only the emitter tube, the lens is positioned wall between the emitter and supply tubes, the lens is moved to the second position. When the lens is in the second position, it is focussed such that during the sweep time of the beam along the diameter of the lens, there is perforation made of the emitter tube and the wall common to the emitter and supply tube. The focal point of the beam is substantially incident to the common wall between the emitter and supply tubes.The described embodiments set forth that the focal point is substantially incident with the common wall or emitter tube, this means that the hole size can be varied by adjusting the position of the focal point, changing the output of the laser and adjustment of the pulse length or any combination thereof.

In yet another embodiment of the invention, the apparatus is generally of the same configuration as in the first described embodiment, however, it accomplishes perforation of the emitter tube alone and the common wall between the emitter and supply tubes, but does not use a movable lens as set forth in one of the above described embodiment.

In this embodiment of the invention, the lens is a split lens of essentially single configuration with a diameter that is greater that for the lens used in the above described embodiments. The split lens is one in which the lens has a first and second portion, each having a configuration of substantially one-half of this lens. The first portion is positioned such that it focuses the incoming beam at or near the surface of the emitter tube.

The second portion of the lens is positioned such that it focuses the incoming coherent light beam at or near the common wall between the emitter and supply tubes, thus effecting perforation of both emitter and supply tubes to the desired hole size.

When this embodiment is used, the beam is timed such that when only the emitter tube is desired to be perforated, the beam is swept across the portion of the diameter associated with the first portion of the lens. When it is desired to perforate both the emitter and supply tubes, the beam is timed such that when reflected from the rotating polysided mirror it is swept across the diameter of the lens associated with the second portion of the lens.

The system of the invention also contemplates the use of an improved apparatus to determime when the proper perforation size has been made.

This is accomplished with a system using a photodetector which is positioned near the perforation site. When high intensity coherent light impinges on the tube surface, a certain degree of reflection takes place regardless of the color of the tubing. The photodetector senses the light and when a certain hole size is made, the amount of reflected light received by the photodetector, consistent with that hole size, is found. The photodetector is connected with to a signal processor which is responsive, and converts the detected signal to drive a meter to indicate the hole size.

An object of the invention is to provide an improved system for perforating moving materials.

Another object of the invention is to provide an improved system utilizing a laser for perforating moving material where the lens is movable to effect perforating one or a plurality of thicknesses of material.

A still further object of the invention is to provide an improved laser drilling system for perforating moving material utilizing a split lens that can perforate one or a plurality of thicknesses of moving material.

A further object of the invention is to provide a system for perforating moving material including improved hole size detection and control means.

Description of the Drawings Figure 1 is a schematic illustration of an embodiment of the system of the invention for perforating holes in moving material.

Figure 2 shows schematically another embodiment of the system of the invention to perforate a first surface and a first and second surface of the moving material.

Figure 3 shows schematically an embodiment of the invention for perforating holes in a first surface and a first and second surface of moving material where the focussing lens is a split lens.

Figure 4 is an elevation view of an actual embodiment of the apparatus for moving the lens of Figure 2.

Figure 5 illustrates another embodiment of an apparatus to move the lens as shown in Figure 2.

Figure 6 illustrates a system to detect perforation hole size.

Detailed Description of the Drawings Figure 1 shows the basic embodiment of a system 1 for perforating moving material such as thermo-plastic pipe for irrigation. Laser or coherent light source 2 has connected thereto a timer 4. The timer 4 is used to determine pulse duration and the interval between light pulses.

Coherent light 6 from laser 2 is directed to a polysided mirror 8. The polysided mirror in the illustrated embodiment of the invention has twelve sides. The mirror 8 is rotated in direction "E" and the pulses of light from laser 2 are timed by timer 4 such that the light 6 is incident on one of the faceted faces of the polysided mirror 8 and thereafter is reflected through focussing lens 10.

Lens 10 is aligned so that its axis 12 is perpendicular to workpiece 12, in this case irrigation tubing. Tubing 12 is transported by suitable means (not shown) in direction "A". The light reflected from rotating polysided mirror S is timed so that the duration of the light pulse in conjunction with the rotation of mirror 8 in direction "E" causes the reflected beam to sweep along the diameter of lens 10. The sweeping of the beam along allows the focal point 18 of the beam, after passing through lens 10, to move in a substantially horizontal plane. As is shown in Figure 1 , the beam's focal point 1 8 travels a distance "D" representing the travel of the beam during the sweep to a point 18' shown by the phantom lines which indicate the cut-off point of the light pulse.

The use of a lens 10 in combination with rotating reflector S results in the linear movement of the focal point of the laser beam of the tube 1 2.

To provide sufficient time for the focused beam of coherent light to perforate the moving material, the sweep rate of the focal point must match the movement rate of the tubing 12 in direction "A'-. It is through the sweep of the focal point, which remains directed at a discrete spot on tubing 12 because of the matched movement of the beam sweep and movement rate of the moving material, that the perforation is made.

The thermo-plastic irrigation tubing 1 2 has two tubes. The first tube is emitter tube 14 and the second tube is supply tube 1 6. The two tubes have a common wall 1 7. The tubes have perforations such that the supply tube 1 6 supplies fluid to emitter tube 14. The emitter tube in turn provides perforations for egressing the fluid for irrigation.

The spacing of the perforations in emitter tube 14 and the common wall between emitter tube 14 and supply tube 1 6 are different. As such there must be a perforating scheme which can do two things. The scheme must have the ability to perforate the emitter tube or both the emitter tube 14 and the common wall between emitter tube 1 4 and supply tube 1 6 simultaneously. The perforation made by the focussed beam at 18 is made in upper tube 14 of the thermo-plastic tubing configuration, generally shown at 1 2.

Figure 2 shows a system 19 for perforating holes in moving material where the perforations are to be accomplished in two thicknesses of tube material, such as tubing 12.

The system of Figure 2 accomplishes the required action of either perforating a single thickness, emitter tube 14, or two thicknesses, emitter tube 14 and wall 17, of the moving material. Lens 10 is positioned in one of two positions to effect perforation of either emitter tube 14 alone or emitter tube 14 and common wall 17 between emitter tube 14 and supply tube 16. To accomplish these tasks suitable means (not shown) is used to move lens 10 in direction "B" to a lower position.

This lowers the focal point to a lower position 20 within the tubing 12. As a result perforation of emitter tube 14 and common wall 17 between emitter tube 14 and supply tube 16 is effected.

The focal point sweeps with the moving material to point 20' where it is cut off. After the double thicknesses of moving material is perforated, the lens 10 is moved in direction "C" back to its the original position for perforating only emitter tube 14.

There is no set ratio of outer to inner holes.

There can be five holes perforated in the emitter tube to every one in the common wall 17. This is merely the designers choice.

As stated, the spacing of the perforations in emitter tube 14, on the one hand, and common wall 17 on the other hand, is different. When it is time to perforate the emitter tube 14 only, the tens 10 is in the up position. When it is time for perforation of common wall 17 between emitter tube 14 and supply tube 16 the lens 10 is moved in direction "B" to a second position. Perforation of single or double thicknesses are accomplished in one sweep.

The system 21 shown in Figure 3 can perform the same operations as were described for the system of Figure 2 except that there is no need to move the lens 10 to accomplish perforations in more than one thickness substantially simultaneously.

Lens 10 of Figure 2 is replaced by lens 50 which is a split lens having first and second portions 51 and 53, respectively. The lens 50 is generally double the diameter of the previously described lens 10. The first portion 51 is used to focus the beam at 52 for perforation of the emitter tube 14 only. The second portion 53 of split lens 50 focusses the beam at 54 for perforation of both emitter tube 14 and the common wall 17 between emitter tube 14 and supply tube 16. The use of the split lens 50 to accomplish the required perforating actions eliminates the need to move the lens from the first position to the second position when it is desired to perforate more than one thickness of moving material.

Figure 4 shows an apparatus 100 for shifting positions of lens 10 of Figure 2. It has support member 101 to which is attached solenoids 102 and 104. Push rods 106 and 108 correspond to solenoids 102 and 104, respectively. The solenoids 102 and 104, via push rods 106 and 108, drive lever 110 which turns about pivot point 115. Lever 110 has openings 112 and 114 for receiving solenoid push 106 and 108, respectively. The openings 112 and 114 are elongated to allow for the double movement of the lever 110 since it operates in a flip-flop mode as will be described.

At the end of lever 110 is roller bearing 116, which fits into opening 120 of member 118.

Member 118 is attached to bar 121. Bar 121 is the acting member which is connected to lens support member 124 accomplishing the movement of the lens 10 as shown in Figure 2.

Bar 121 pivots about pivot point 119. Connected to bar 121 at an end opposite the one where the lens holder 124 is dash pot 122 used to dampen the motion of the bar when the lens is to be moved.

The opening 120 of member 118 is shaped so that as bearing 11 6 moves by the action of the solenoids 102 or 104, the bar is pushed upwards which causes the lens holder 124 containing the lens to move to the down position. The roller then goes through a dwell with the lens holder in the down position and the lens holder 124 is returned to the upper position upon completion of movement of the roller in groove 120. The up and down movement are repeated by the next movement of the roller through slot 120.

The solenoids 102 and 104 are used to effect the proper movement of lever 110. As is shown in Figure 4, for the next cycle of the movement of the lens holder 124, the solenoid 104 is actuated and solenoid rod 108 pulls the lever toward solenoid 104, thus moving the lever in specifically timed motion through the entire cycle for moving the lens holder 124 first down and then up.

In each movement of the bar about pivot point 119, the the dash pot 122 dampens out any vibrations which would be present by mere movement of the bar. Additionally, the spring 126 is disposed at the connection point of the holder 124 and bar 121 and is used to connect the lens holder 124 to bar 121. Spring 127 preloads the lens holder 124 in the upward direction.

Figure 5 at 200 shows another embodiment of an apparatus for shifting position of the lens in Figure 2 to different positions. The apparatus has support member 201 to which is attached solenoid 202. Solenoid 202 has solenoid push rod 208. The solenoid push rod 208 contacts bar 204 which pivots about point 210. As the bar 204 is pushed in the upward direction by solenoid push rod 208, the opposite end of bar 204 pushes lens holder 214 in a downward direction. At the point where the bar contacts the lens holder 214 the adjustment screw 212, threadably engages the end of the bar. The screw 212 adjusts the lens for proper position of the focal point of the lens. When the lens holder 214 is in a down position spring 216 is depressed. When the solenoid is deactivated lens holder 214 returns to its original position by the extension of spring 216.Attached to the opposite end of rod 204 is dash pot 206 which dampens out any vibrations found in the movement of the lens holder and bar.

Figure 6 shows a system for detecting specific perforation sizes. The system is connected to a meter 310 and /or to the laser 2 for providing a feedback to the laser for maintaining optimum conditions so that specific perforation sizes are realized. The system consists of photodetector 304 connected to signal processor 308. The signal processor connects to meter 310 and /or the laser (connection not shown) in Figure 6.

The irrigation tube 12 is illuminated by another laser beam 302 or other high intensity light and there is some reflection of the beam by the surface of the emitter tube 14. The photodetector 304 is disposed close to the illuminated area 305 on the surface of emitter tube 14. This amount of reflection which is received by photodetector 304 will provide an input to signal processor 308.

Signal processor 308 converts the signal to one usable to drive the meter. The reflected light detected by detector 304 is reduced in accordance with an increase in hole diameter.

Since the total area is no longer reflecting light, there is a decrease in the signal output from the photodetector to signal processor 308.

The signal processor is able to determine when a specific level of reflectivity is reached which represents a certain size hole. The signal processor provides an output to drive a meter and the meter will indicate the hole size. This provides an accurate method by which actual perforation size is determined in real time which is far better than existing methods of determining same. Correction of subsequent hole sizes can be effected by changing laser power level and/or pulse length.

Although the perforation of more than one thickness is described for perforating thermoplastic tubing, the invention is not limited to only perforating this type of material. Any other type of moving material can be substituted for the thermo-plastic tubing.

The inventors contemplate the invention all that is shown, disclosed and described to be the invention. However, there can be various adaptations, alterations of the invention which fall in the contemplated system, apparatus or method of the herein described invention. Thus the inventors contemplate the invention all that is shown, described and disclosed to be the invention and all equivalents thereto.

Claims (16)

1. A system for perforating material comprising: a laser; a lens having its axis aligned perpendicularly with the material to be perforated; means for transporting the material to be perforated at a predetermined rate; and means for sweeping the laser beam across and through the lens at a speed whereby the laser beam is directed to a same point on the moving material for a sufficiently long period of time to perforate it.

2. The system as recited in Claim 1 including means for interrupting the laser beam after each perforation of the material.

3. The system as recited in Claim 2 wherein the means for sweeping the laser beam across the lens at a predetermined rate and for directing the laser beam through the lens includes a polysided reflector.

4. The system as recited in Claim 3 including means for moving the lens in a direction along its axis, to vary the focal point between a first and second focal point.

5. The system as recited in Claim 3 wherein the lens has a first and second portion whereby the laser beam directed through the first portion of the lens focusses the beam at a first focal point and the laser beam directed through the second portion of the lens focusses the beam at a second focal point.

6. The system as recited in Claims 4 or 5 wherein monitoring and feedback means comprising a photodetector and signal processor and the system having means connected to the laser for detecting the perforation size and providing feedback to the laser for maintaining proper hole size.

7. A system for perforating irrigation tubing having an emitter tube and a supply tube joined by a common wall comprising: a laser; a lens having its axis aligned perpendicularly with the irrigation tube; means for transporting the irrigation tube to be perforated at a predetermined rate; means for sweeping the laser beam across and through the lens at a predetermined rate whereby the laser beam is directed to the same point on the irrigation tube for a sufficiently long period of time to perforate it.

8. The system as recited in Claim 7 including means for interrupting the laser beam after each perforation of the irrigation tube.

9. The system as recited in Claim 8 wherein the means for sweeping the laser beam across the lens at a predetermined rate and for directing the laser beam through the lens includes a polysided reflector.

10. The system of Claim 9 including means for moving the lens in a direction along its axis to vary the focal point between a position where the focal point is at or near a surface of the emitter tube and the focal point is at or near the common wall between the emitter and supply tube.

11. The system as in Claim 9 including a telecentric lens having first and second portions, said first portion having a focal point at or near surface of the emitter tube and the second portion having a focal point at or near the common wall whereby the laser beam perforates the emitter tube when the beam is directed through the first portion of the lens and the laser beam perforates the emitter tube and the common wall when directed through the second portion of the lens.

12. The system as recited in claim 10 or 11 including monitoring and feedback means further comprising a photodetector and signal processing means and the system with means connected to the laser for detecting the perforation size and providing feedback to the laser for maintaining proper perforation size.

13. A method of perforating a material, said method comprising the steps of generating a beam of coherent radiation; impinging said beam at a focusing means; focusing said beam at a focal point by said focusing means: sweeping said beam across said focusing means; moving said focal point in a focusing line as a result of said sweeping step; moving said material substantially along said focusing line; and timing the movement of said focal point to substantially coincide with the movement of said material; whereby the beam is directed to a same point on the moving material for a sufficiently long -period of time to perforate it.

14. 'The method of Claim 13 further comprising the step of interrupting the beam after each perforation of the material

15. The method of Claim 14 further comprising the step of detecting the size of each perforation; and providing feedback to the generating means for maintaining the proper perforation size.

16. The method of Claim 15 further comprising the step of moving said focusing means in a direction perpendicular to said focusing line between a first and second position; whereby said focusing line is moved between a first and a second position.