US3283120A

US3283120A - Apparatus for working materials with a beam of charged particles

Info

Publication number: US3283120A
Application number: US353324A
Authority: US
Inventors: Spruck Helmut
Original assignee: United Aircraft Corp
Current assignee: Raytheon Technologies Corp
Priority date: 1963-03-23
Filing date: 1964-03-20
Publication date: 1966-11-01
Anticipated expiration: 1983-11-01
Also published as: DE1225775B; NO119619B; BE645421A; GB1044056A; NL6403042A; CH419370A; FR1388356A

Description

Nov. 1,1966 H. SPRUCK 3,283,120

APPARATUS FOR WORKING MATERIALS WITH A BEAM OF CHARGED PARTICLES Filed March 20, 1964 2 Sheets-Sheet 1 HTTOE/VEY Nov. 1, 1966 H. SPRUCK APPARATUS FOR WORKING MATERIALS WITH A BEAM OF CHARGED PARTICLES 2 Sheets-Sheet 2 Filed March 20, 1964 F/GZ F/io

Wl/l/ Ill/4? mmmm H51 M07 JPPUCK 5y a UM Mi HTTflE/VEV United States Patent 8 Claims. or. 219-121 This invention relates to working a material with a beam of charged particles, and particularly to performing operations such as welding, cutting, melting, evaporating, or machining on any material with an electron beam.

In prior art apparatus which are used to work materials with a beam of charged particles, the beam of charged particles is focused by means of an electromagnetic lens on the workpiece to be treated. For this purpose, the current which flows through the focusing lens is adjusted manually while the area of the workpiece on which the electron beam impinges is being watched through an observation device. The lens current which flows through the focusing coil is usually so adjusted that th impingement point of the electron beam has its narrowest cross-section on the surface of the workpiece.

Such an adjustment of the focusing of the beam is inconvenient and time consuming and is, furthermore, inherently affected with subjective errors. If during the Working operation the accelerating voltage or the beam current set at the beginning of the working operation is changed due to a variation in the thickness or composition of the workpiece, the focusing of the beam changes also and therefore it is necessary, while constantly observing the impingement point of the beam, to manually re-adjust the lens current passing through the focusing lens. This necessity of re-adjusting the focusing action arises also when the surface of the workpiece treated has a relief-type shape. In this case there occurs a change in the working distance, i.e. the distance between the lower edge of the focusing lens and the surface of the workpiece. Such a change of the working distance requires a re-adjustment of the focusing of the electron beam.

As may be seen easily, constant observation of the workpiece coupled with a constant control of the focusing of the beam is fatiguing and tiresome to the operator of the apparatus.

It has already been proposed to carry out the focusing of the electron beam automatically. In the prior art, the refractive power of the focusing lens is varied periodically and the quantity of the charged particles coming from the workpiece is measured. As soon as this quantity reaches an extreme value the magnitude of the'current which flows at this moment through the focusing lens is held constant. This method can not be continuously practised during the entire working operation but it is repeated at periodic intervals during the working operation. Furthermore only a relatively small variation of the focusing of the beam may be registered during this process.

The present invention relates to a process for treating a workpiece by means of a beam of charged particles focused on the workpiece by an electromagnetic lens and is characterized particularly in that the proper focusing of the electron beam is constantly maintained independently of changes in machine adjustments and working distance. The present invention is based on the observation that during the Working of the materials by means of an electron beam first the accelerating voltage, the beam current and the working speed are set, and that during the course of the working operation in most instances only the working distance. will change. According to the new Patented Nov. 1, 1966 process the current which flows through the focusing lens is initially automatically adjusted in relation to the values of the accelerating voltage, the beam current and the working distance to the value required for the focusing of the electron beam, and the working distance is constantly measured during the working operation and the current flowing through the focusing lens is adjusted in relation to this measurement.

In this novel process it is therefore necessary to ad just for example by means of two control knobs the values of the accelerating voltage and the beam current determined on the basis of the properties of the workpiece before the actual start of the working operation. Furthermore the predetermined working distance is set at a special setting knob. Together with these settings the device for generating the current flowing through the focusing lens is influenced in such a manner that it supplies a lens current set to the proper value, that is to say, when the operation begins the electron beam is focused on the surface of the workpiece. If during the working operation a change of the working distance occurs, this change is registered constantly and simultaneously the current flowing through the focusing lens is constantly re-adjusted in such a way that the proper focusing of the beam is maintained.

It is advantageous to carry out the measuring of the working distance by optical means. In this case the measurement of the working distance is obtained continuously and automatically and the measured values regulate automatically the current flowing through the focusing lens.

An optical measurement of the Working distance presupposes that the electron beam is in operation and that accordingly its impingement point is brightly illuminated with respect to the dark surrounding area.

The adjustment of the working distance before the start of the working operation is obtained by an adjustment to the approximate value, this value being obtained from the known distance between the workpiece support and the lower edge of the lens and the thickness of the workpiece.

After starting the apparatus the proper value of the working distance is then measured automatically and the lens current supply device is automatically so influenced that the focusing of the beam is correctly adjusted.

It is also possible to arrange a tungsten strip at the level of the workpiece surface, to operate the beam and to measure the bright spot produced on the strip. In this manner the focusing of the electron beam which is correct for the measured working distance is assured. After disconnecting the beam the tungsten strip may be re placed by the workpiece and thus the beam is focused correctly on the workpiece surface at the beginning of the working operation.

Under certain conditions it is also possible to produce before the start of the Working operation by means of a regular flashlight a light spot on the workpiece surface and to measure this light spot with the optical distance meter. In this manner it is obtained that already at the moment of starting the apparatus the exactly correct working distance is set.

The arrangement according to the invention consists of a known apparatus for working materials by means of an electron beam which is provided with an electromagnetic lens for focusing the electron beam. A lens current supply device is provided for the purpose of supplying current to the focusing lens. Means for determining the magnitude of the lens current are connected to means for adjusting the accelerating voltage and the beam current. Furthermore an optical distance meter for measuring the working distance is provided, this distance meter being also connected to the lens current determining device.

In many cases it is necessary to set the focusing point of the electron beam in such a way that it does not lie exactly on the workpiece surface but so that it lies a certain distance above or below this surface. As a novel feature of this invention, a control member is connected to the lens current supply device for the purpose of adjusting the axial position of the focusing point. By means of this control member the axial position of the focusing point may be displaced as desired without influencing the remaining automatic adjustment of the focusing point in any manner.

The optical distance meter is preferably so designed that it measures the bright spot produced by the electron beam on the workpiece and generates in the plane of a photocell two pictures of this spot which coincide to form a double image upon reaching the balanced state. In the photocell plane, tWo photocells are provided Whose separation line coincides with the center line of the double image. These photocells are connected to a readjusting device which brings the distance meter always into the balanced position.

The invention will be explained hereafter in greater detail by means of an embodiment illustrated in the accompanying drawings in which like reference numerals refer to like elements in the various figures and in which:

FIGURE 1 shows diagrammatically an embodiment of the apparatus according to the invention.

FIGURE 2 shows diagrammatically an embodiment of the lens current supply device incorporated in FIGURE 1.

FIGURE 3 shows a partial section of another embodiment of the apparatus according to the invention.

The apparatus for working materials by means of an electron beam illustrated in FIGURE 1 shows the cathode 1, the control cylinder 2 and the grounded anode 3 of the beam generating system. In device 4 a high voltage of about 100 kv. is generated and supplied by means of a high voltage cable to device 5. This device is adapted to produce the adjustable heating voltage and the adjustable control cylinder bias voltage. These voltages are conducted over a high voltage cable to the beam generator system 1, 2, 3.

A control member 6 is connected to device 4 and is adapted to adjust the value of the high voltage. Another control member 7 is connected to device and is adapted to adjust the control cylinder bias voltage and thus the adjustment of the beam current.

Below anode 3 viewed in the direction of the beam a magnetic deflecting system 8 is mounted which is adapted to adjust the electron beam 10. Deflection voltage generator 9 feeds current to the deflecting system 8.

Below the deflecting system 8 a screen 11 is mounted which may be moved by means of knobs 12 and 13 in the plane of the drawing and also perpendicularly to the plane of the drawing. After the adjustment of the electron beam it passes through the screen 11 and is focused by means of the electromagnetic lens 14 on the workpiece 16 arranged in the work chamber 15.

An electromagnetic deflecting system 17 arranged be low the focusing lens 14 is supplied with current from lens current generator 18 and is adapted to deflect the electron beam 10 relative to the workpiece 16.

The workpiece 16 is placed in work chamber on a cross-table 19 which may be moved by means of hand wheels 20 and 21 in the plane of the drawing and perpendicularly to the plane of the drawing. In place of hand wheels 20 and 21 electric motors may be provided which carry out the movement of the workpiece 16.

Above the electromagnetic lens 14 an optical lens 22 is mounted which is movable in the direction of its optical axis. This lens is provided with a bore into which a tube 23 is placed. Electron beam 10 passes through this tube 23. The lens 22 is moved in the axial direction by means of an electric motor 24 and a drive 25. Above lens 22 a mirror 26 is mounted which has an opening allowing the passing of the electron beam 10. The electron beam 19 generates on the surface of the workpiece 16 a brightly illuminated spot. The light emitted from this spot passes through lens 22 and is projected over the mirror 26 to a pair of photocells 27 and 28. Between the mirror 26 and the photocells 27, 28 an additional lens 29 is mounted which produces in the balanced state a coinciding double image of the illuminated spot on the workpiece 16 in the plane of the photocells 27, 28. In a beam portion of the light reflected by mirror 26 a filter element 30 is mounted.

Behind the photocells 27, 28 a bridge connection 31 is provided which is connected to the electric motor 24. The electric motor 24 provides the axial displacement of the lens 22 and also the actuation of the control member 32.

The control member 32 and the two control members 6 and 7 are connected to a lens current supply device 33. This device furnishes the current flowing through the focusing lens 14. Additional control member 34 is connected to the lens current supply device 33 and is adapted to adjust the axial position of the focusing point of the electron beam 10.

The lens current supply device 33 is illustrated diagrammatically in FIGURE 2. It consists essentially of the potentiometers 35, 36 and 37 and of the battery or power supply 38. To adjust the lens current the sliders 39, and 41 are moved. It is also possible .to rotate the potentiometer 37 relative to its slider 41 and this is irzme by means of the control knob 34 via driving gears The operation of the apparatus is as follows: Before starting the working operation and based on the properties of the workpiece the accelerating voltage is set by means of control 6 and the beam current by means of bias voltage control 7. By means of control 6 the slider 39 and by means of control 7 the slider 40 are moved in the lens current supply device 33. The work distance is thereafter set by means of control 32 whereby slider 41 is moved. The

controls

6, 7, 32 and 34 co-operate with dials not shown in the drawing. After controls 6, 7 and 32 are set such a resistance value is established across potentiometers 35, 36 and 37 that the lens current supplied from source 33 to focusing lens 14 produces a focusing of the electron beam 10 on the surface of the workpiece 16.

When the working distance changes after the electron beam 10 has been operated, the optical arrangements 22, 26, 29 produces in the plane of the photocells 27, 28 no coinciding double image of the illuminated spot on the workpiece 16. The two images deviate from the center by opposite equal amounts. By means of filter 30 it is obtained that one of the photocells 27, 28 receives less light than the other cell. Due to this, the bridge 31 becomes unbalanced and the electric motor 24 receives current. This moves lens 22 over drive 25 in the axial direction until, in the plane of the photocells 27, 28, a coinciding double image is reestablished. This movement of the lens 22 is simultaneously transferred over control 32 into the lens current supply device 33. The slider 41 on potentiometer 37 is thereby displaced and the current through focusing lens 14 is varied in a direction which refocuses the electron beam at the surface of the workpiece 16 in spite of the changed working distance.

In the case where the focusing point of the electron beam 10 lies above or below the surface of the workpiece 16 this displacement is fed into the lens current supply device 33 by means of the control 34. By means of con trol 34 the potentiometer 37 is rotated as a whole over drive 42 relative to slider 41. Thus the current flowing thnough the focusing lens 14 is changed to a small extent and this change causes a displacement of the axial position of the focusing point.

In the example illustrated in FIGURE 3 an optical distance meter is arranged in the work chamber 15 below the focusing lens 14. This distance meter consists of mirrors 50 and 52 and

lenses

54 and 56. is designed to be semi-transparent.

The distance meter is so .set that it produces, in the balanced position, in the plane of two photocells 58, 60 a coinciding double image of the illuminated spot on the workpiece 16. If the working distance changes a coinciding double image is no longer created in the plane of the cells 58, 6t) and the two partial images deviate from each other. Due to this, one of the two photocells 58, 60 receives more current than the other cell and the associated bridge connection 62 starts to operate. Over this bridge connection the electric motor 64 receives current and this motor rotates over the flexible shaft 66 the mirror 52 until in the plane of the photocells 58, 60 again a coinciding double image is obtained. Simultaneously with the rotation of the mirror 52 the control 32 of the lens current supply device 33 is actuated. The electron beam may impinge continuously on the workpiece 16. However, in many cases it is advantageous to select instead of a continuously impinging beam a beam which is effective in a pulsating manner. This pulse-like effect of the beam does not disturb the optical distance measurement because the impulses are kept so short that no change occurs in the illuminated spot on the surface of the workpiece 16.

The present invention is particularly suitable for application in apparatus for milling, cutting, soldering or welding by means of an electron beam. In all these cases the workpiece is moved continuously relative to the electron beam so that upon a change in the working distance a continuous readjustment of the focusing action is necessary. The present invention finds also appropriate application in apparatus for drilling by means of an electron beam. If in such applications several holes are to be drilled in a workpiece at different locations it is not necessary to re-adjust manually the focusing action between the diiferent holes because also in this case an automatic re-adjustment takes place.

What is claimed is: 1. Apparatus for working material with an energized beam comprising:

means for generating an energized beam, means for focusing said beam at a material to be worked,

means for optically measuring the working distance between said focusing means and the material to be worked and for generating a signal indicative of a variation in said working distance from a desired value, and

means responsive to said signal indicative of a variation in working distance for controlling said focusing means whereby said beam is maintained focused at the material to be worked.

2. The apparatus of claim 1 wherein said means for generating an energized beam comprises:

a source of charged particles,

The mirror 52 means for accelerating the charged particles from said source toward a material to be worked, means for forming said accelerated particles into a beam, and means for controlling the beam current. 3. The apparatus of claim 2 wherein said focusing means comprises:

an electromagnetic lens for focusing the beam of charged particles. 4. The apparatus of claim 3 wherein saidmeans for controlling the focusing means comprises:

an adjustable lens current supply, and means responsive to said signal indicative of a variation in working distance for varying the current flowing from said supply through said electromagnetic lens. 5. The apparatus of claim 4 further comprising: means coupling said particle accelerating and beam current controlling means to said lens current supply whereby adjustment of the beam current or particle acceleration varies the lens current. 6. The apparatus of claim 5 wherein said optical working distance measuring means comprises:

mean for sensing the illuminated spot produced on the material being worked by the beam and for producing two images thereof, and light sensitive means responsive to the images produced by said sensing means for generating an electrical signal indicative of a variation in working distance when said images do not coincide. 7. The apparatus of claim 6 wherein said sensing means comprises:

optical system having a variable focal length, means responsive to the signal generated by said light sensitive means for varying the focus of said optical system, and an optical filter positioned between said optical system and said sensing means for attenuating one of said images. 8. The apparatus of claim 7 wherein said light sensitive means comprises:

two photocells whose separation line coincides with the center line of the coinciding images, and means connecting said plhotocells as legs of a bridge circuit whereby an electrical output signal in generated whenever the images do not coincide.

References Cited by the Examiner UNITED STATES PATENTS 2,304,814 12/1942 Glasser 88l 2,472,951 6/1949 Klinke 318480 X 2,945,132 7/1960 Schuoh 250222 X 3,037,423 6/1962 Shurclifl? 881 3,158,733 11/1964 Sibley 219-121 X JOSEPH V. TRUHE, Primaly Examiner.

Claims

1. APPARATUS FOR WORKING MATERIAL WITH AN ENERGIZED BEAM COMPRISING: MEANS FOR GENERATING AN ENERIGIZED BEAM, MEANS FOR FOCUSING SAID BEAM AT A MATERIAL TO BE WORKED, MEANS FOR OPTICALLY MEASURING THE WORKING DISTANCE BETWEEN SAID FOCUSING MEANS AND THE MATERIAL TO BE WORKED AND FOR GENERATING A SIGNAL INDICATIVE OF A VARIATION IN SAID WORKING DISTANCE FROM A DESIRED VALUE, AND MEANS RESPONSIVE TO SAID SIGNAL INDICATIVE OF A VARIATION IN WORKING DISTANCE FOR CONTROLLING SAID FOCUSING MEANS WHEREBY SAID BEAM IS MAINTAINED FOCUSED AT THE MATERIAL TO BE WORKED.