US3255670A - Electric tracer for profiling machine tools - Google Patents

Description

June 14, 1966 F. LASERMANN ELECTRIC TRACER FOR PROFILING MACHINE TOOLS Filed Feb. 5, 1965 5 Sheets-Sheet 1 lnvenfar: FfLasermcmn A-r-rokNEas June 14, 1966 F. LASERMANN 3,255,670

ELECTRIC TRACER FOR PROFILING MACHINE TOOLS Filed Feb. 5, 1965 5 Sheets-Sheet 2 Fig. 2

Fig. 4

Inventor.- ELczser/mlnn f org/W ATTORNEHS June 14, 1966 F. LASERMANN ELECTRIC TRACER FOR PROFILING MACHINE TOOLS 5 Sheets-Sheet 5 Filed Feb. 5, 1965 Fig. 3

lnvenior: F. Lasermcm United States Patent O 9 Claims. or. 90-62) The present invention relates to profiling machine tools and particularly to an electrical tracer for machines of this type. Tracers of this type are suitable for all types of profiling work, particularly for planetary milling, rapid return milling and profile milling. I

An object of the invention is to improve the precision of a profiling procedure, so that the errors produced by the tracer during the sensing of a shape, are reduced or completely compensated.

According to the present invntion, an electric tracer for profiling machine tools comprises a tracer point held in a ball'and socket joint and issuing above said joint into a casing, said casing acting on a swash plate for forward movement, four mutually opposite sensing members ar-.

ranged on said swash plate symmetrically to the axis of said casing, said members producing one set of electric signals proportional to the deflection of the tracer point and a core rod disposed along the axis of said casing, an extension of said core rod acting upon sensing means to produce another set of electric signals proportional to its deflection, said other set being superimposed on said one set of signals so as to reduce deflection errors of the tracer point. The sensing members arranged on the swash plate may be constructed asiron-cored magnets, which are rotatable with the swash plate opposite its armature coil disc attached to the core rod. The ironcored magnets are suitably located with their pole surfaces in a plane parallel to the axis of the tracer casing and the pole surfaces of the iron-cored magnets are suitably located on the surface of a cylindrical jacket, which surrounds the rarmature coil discs.

According to another embodiment of the invention, the sensing members arranged on the swach plate consist of quadrants, over which armature coils are arranged on a disc rotatable about the core rod. This disc is rotated by an adjusting motor, secured to the core rod and controlled .by the corrector signals of the sensing members on the core rod, in the sense of a reduction of the deflection error relative to the armature discs. The sensing means on .the core rod preferably consists of an armature disc, which is reciprocably movable between two fixed armature coils in the direction of its axis, during the deflecting movements of the core rod. A mechanical barrier is arranged .on the tracer casing, which barrier while in operation connects casing and core rod, so that the forward movements of the swash plate are prevented.

The invention may be understood more fully from the following description of specific embodiments with referece to the accompanying drawings wherein:

FIGURE 1 is a vertical section through a tracer according to the invention;

FIGURE 2 is a section along the line 11-11 of FIG- URE 1;

FIGURE 3 is a vertical section through another embodiment of a tracer according to the invention;

FIGURE 4 is a section along the line IV-IV of FIGURE 3.

The profiling tracer according to the invention comprises in known manner a tracer point 1, which is fixed in a ball-and-socket joint 2, and issues above the balland-socket joint into :a tracer casing 3. A core rod 4 is arranged within said casing 3, which rod is supportedwith ball sockets and balls 5 on its lower end in the centre of the ball-and-socket joint 2. The casing 3 ends somewhat in the middle of the core rod 4 and is connected during the deflection movements of the tracer point 1 to its annular head 6 arranged on the upper end, only after :a certain forward movement has been covered, against a flange 7 on the core rod. Inthis way, a very delicate, doubled lever transmission is achieved in a very limited space in addition to the forward movement.

The annular head 6 on the upper end of the tracer casing 3 is located outwardly free from play against a casing projection 8 of a swash plate 9 The swash plate 9 is pivotally arranged on the core rod 4 by means of the ball-and-socket joint 14 and is held in 'its central position by means of a disc washer 11, which is securely connected to the core rod 4, and by means of a cap disc 10 supported by springs 13.

Approximately quadrant- shaped armature discs 16 and 17 are arranged near the periphery of the swash plate 9. These four armature discs are located symmetrically to the axis of the tracer. A disc 18 is rotatably fixed to the core rod 4 above the swash plate, on which disc mag netic coils 19 and 20 are arranged in such a way that they lie opposite one another, and are also symmetrical to the axis of the tracer and one of the magnetic. coils being always assigned to an armature disc 16 or 17. Said armature discs and magneic coils form the sensing members which produce sigals when the tracer point 1 is deflected. Two opposite sensing members always form a half-bridge, the second half-"bridge being located in the control part and the variable distance of the armature disc 16 or 17 from the armature coil 19 or 20, producing signal voltages, which correspond in size and polarity to the direction of the tangent of the scanned model contour. Said signal voltages are conveyed to the amplifier and are used for controlling the servo-motors in the X and Y coordinates.

The upper end of core rod 4 is also held by a ball 21 secured in ball sockets. The upper support 22 of the core rod issues into a rod 23, which is guided in a fixed bearing 24, so that it may effect only axial movements. A spring 25 is arranged above the rod 23, which spring is also supported against a fixed bearing 26 and presses the bar 23 in line on the bearing of the core rod. An armature disc 27 is secured to the rod 23, which disc is reciprocably movable between two secured armature coils 28 and 29. This armature disc 27 forms with both magnetic coils 28 and 29 another sensing means, the signals of which on the one hand superpose the signals of the sensing members on the swash plate 9 and on the other hand serve to control a motor 30, which is arranged 'near the upper end of the core rod 4 and with a reduction gear 31, the rotatable disc-18 with the armature coils 19 and 20 located thereon, may rotate about a quarter turn according to the signals received by the sensingmembers 27 and 29.

On the casing 3 is arranged a disc casing 32, by means of its balls 33 or even locking wedges which are set in the casing wall, maybe pressed against the core rod 4. This casing 32, together with the balls 73, forms a mechanical lock, it it is shifted upwards corresponding to the diagrammatical drawing, and connects casing and core rod securely together, so that forward movements of the swash plate 9 are stopped. Such a locking of the forward movements is desired, for planetary milling or rapid return milling. I

A tracer according to FIGURES ,3 and 4 is essentially constructed in a very similar way to the previously described tracer. The same reference numerals are used for the same parts. The construction of the lower part of the tracer with casing 3 and core rod 4 corresponds to that of the above-described example. of the casing 3, a casing 35 is rotatably arranged on ball bearings 34, which casing issues upwardly into a plate 36, which is located at the approximate height of the upper end of the casing, and on which iron-cored magnets 37, 38, 39 and 40 are arranged in such :a way that, in pairs and opposite one another, they subdivide the circular disc 36 into quarter sections. The arrangement of the iron-cored magnets 37 to 40 may be particularly seen from FIGURE 4, which shows a section through this part of the tracer. The pole surfaces 37a, 38a, 39a and 40a of said iron-cored magnets 37 to 40 are arranged in such a way that they are located on a cylindrical jacket surface. This cylindrical jacket surface surrounds a disc 41 with armature discs 42, 43, 44 and 45, which are located opposite the polar surfaces of the iron-cored magnets, always however surrounding about a quarter section of the circular disc 41. Between the armature discs 42 to 45 and the pole surfaces 37a to 40a, there is an air gap. The disc 41, on which the armature discs 42 to 45 are arranged, is firmly fixed on the upper end of the core rod 4.

The rotatably arranged casing 35, with the plate 36 carrying the iron-cored magnets 37 to 40, is rotatable by means of a small motor 30 through a driving pinion 31 and a belt 46 and may be rotated by mean-s of the motor 30 in the same way as the rotatable disc 18 with the magnets 19 and 20 fixed thereon according to the previously described embodiment.

The sensing means 27 to 29 arranged above the core rod 4 is constructed in this embodiment in the same way as in the previously described embodiment.

The function of the first tracer described-above is explained more clearly later. The function of the second tracer described above is similar in every respect:

The tracer point 1 is guided to the template in the direction pre-selected by hand (starting thrust). When the tracer point 1 is in con-tact with the template, the tracer casing 3, which is securely fixed to the tracer point, is swung over the ball-and-socket joint 2. At the same time, by means of the free-from-play addition of the annular bead 6 located at the upper end of the tracer casing 3 against the casing projection 8, a shifting of the swash plate 9 from the central position is produced, namely about an axis parallel to the tangent of the curved form in the mechanism point of the tracer point. Let it be assumed that the tracer point 1 is swung outwardly to the left, then the swash plate 9 tilts about an axis, which stands vertical on the plane of the drawing in the centre of the balland-socket'joint 14, and the right armature disc 16 approaches the opposite armature coil 19 from its normal position, the left armature disc 18 is removed from the opposite armature coil 19, and said coordinate-data sensing members the deliver corresponding signal voltages.

If the tracer point 1 is deflected further, the annular head 6 is located on the upper end of the feeler casing 3 against the flange 7 of the core rod 4 and deflects the core rod. This deflection causes the ball to leave its balland-socket joint so that the bearing distance of the core rod becomes greater. The outer support 22 is put under pressure against the effect of the springZS, and the bearing rod 23 shifts the armature plate 27 secured thereto in line on the upper armature coil 29. The arrangement is such that the armature disc 27 is located very closely above the lower armature coil 28 when the system is in normal position. If, through a deflection of the tracer point 1 the armature disc 27 comes after starting into the central position on the contour of the template the starting thrust is released, and the profiling process is started. The signal of the sensing means 27 to 29 produced when the centre position of the armature disc 7.7 is reached, thus shows the way to the servo-motors for On the upper end the X and Y coordinates even to the signals produced by the sensing members 19, 20 on the swash plate.

As soon as the profiling process has started, an almost tangential movement, opposite the direction of movement, of the signal voltages of the sensing members is produced on the swash plate by the friction of the tracer point on the template. Consequently, the tracer point is deflected more or less after each inclination of the con tour on the template. When the tracer is deflected the armature disc 27 also moves from its centre position and in an upward movement gives a negative signal rising from nil or in a downward movement a positive signal rising from nil. The signals of the sensing means 27 to 29 are superposed on the signals of the sensing members 16, 19 and 17, 20 in the radial forward deflection, so that they are effective in the sense of a reduction of the deviation; i.e., if the tracer 1 is further deflected and the sensing means 27 to 29 releases a rising negative signal, this value is subtracted from the signal of the direction of movement, which may be seen from the reference, and is added to the signal of the direction displaced for this purpose about When the deflection of the tracer point 1 is reduced below the centre position of the axial sensing means 27 to 29, the superimposition results in the opposite sense, it is thus the rising positive signal which is added to the signal of the direction of movement, which is shown in the reference, and subtracted from the signal of the direction displaced for this purpose about 90.

The production of the corrector signal by the sensing means 27. to 29 requires an alteration of the deflection of the tracer and therefore also a deviation of the theoretical contour of the template. Since the value on a 360 circuit is not constant according to experience, that is it is conditioned by variable friction values between tracer point and template as well as frictions in the mechanical part of the tracer as well as on deviations from proportionality of the tracer deflection to the released signal, this tracking error may be compensated by a tracer point offset by a small value. In order to reduce the tracking error still further, the corrector signal produced by the sensing means 27 to 29 is still given to the servomotor 30, which shifts the holding disc 18 with the armature coils 19 and 20 in line to a zero tracking error.

By means of the cited error effects, the tangent of the movement of the tracer point is inclined opposite the tangent of the template in the actual operating position of the tracer point during the profiling process. Both tangents do not correspond The difference of inclination between the actual tangent (of the movement) and the theoretical tangent (of the template) is determined by the sensing means 27 to 29, the error signal of which becomes elfective for correction at two different positions namely once in elfect on the servo motor 30, the error is prevented from exceeding a certain magnitude and in the effect on the sensing members 16, 17 and 19, 29 arranged in the quadrants, a corresponding error is further minimised.

It will be understood that the above-described embodiments are intended to be only by way of illustrative example and that modifications may be made in various ways apparent to those skilled in the art without departing from the scope of the invention, and that this is limited only by the appended claims.

I claim:

1. An electric tracer for profiling machine tools comprising a tracer point held in a ball and socket joint and issuing above said joint into a casing, said casing acting on a swash plate for forward movement, four mutually opposite sensing members arranged on said swash plate symmetrically to the axis of said casing, said members producing one set of electric signals proportional to the deflection of the tracer point and a core rod disposed along the axis of said casing, an extension of said core rod acting upon sensing means to produce another set of electric signals proportional to its deflection, said other set being superimposed on said set of signals so as to reduce deflection errors of the tracer point.

2. An electric tracer according to claim 1, wherein said sensing members are constructed as iron-cored magnets which, with the swash plate, are rotatable opposite corresponding armature discs secured on a disc to said core rod. 1

3. An electric tracer according to claim 2, wherein said iron-cored magnets are arranged with their pole surfaces in a plane parallel to the axis of said tracer casing.

4. An electric tracer according to claim 3, wherein the pole surfaces of the iron-cored magnets are located on the surface of a cylindrical jacket, which surrounds the said disc and said armature discs.

5. An electric tracer according to claim 1, wherein said sensing members comprise approximately quartersectioned armature discs above which armature coils are arranged on a disc rotatably fixed to said core rod.

6. An electric tracer according to claim 5, wherein said disc is rotatable by a servo motor securely fixed to said core rod and controlled by corrector signals from said sensing means, said signals being in the sense of an extension of the deflection error opposite the deflection disc.

7. An electric tracer according to claim 5, wherein said disc is rotatable by a servo motor securely fixed to said casing and controlled by corrector signals from said sensing means said signals being in the sense of an extension of the deflection error opposite the deflection operation, whereby 'the forward movement of the swash plate is locked.

No references cited.

WILLIAM W. DYER, JR, Primary Examiner.

G. A. DOST, Assistant Examiner.

Claims (1)

1. AN ELECTRIC TRACER FOR PROFILING MACHINE TOOLS COMPRISING A TRACER POINT HELD IN A BALL AND SOCKET JOINT AND ISSUING ABOVE SAID JOINT INTO A CASING, SAID CASING ACTING ON A SWASH PLATE FOR FORWARD MOVEMENT, FOUR MUTUALLY OPPOSITE SENSING MEMBERS ARRANGED ON SAID SWASH PLATE SYMMETRICALLY TO THE AXIS OF SAID CASING, SAID MEMBERS PRODUCING ONE SET OF ELECTRIC SIGNALS PROPORTIONAL TO THE DEFLECTION OF THE TRACER POINT AND A CORE ROD DISPOSED ALONG THE AXIS OF SAID CASING, AN EXTENSION OF SAID CORE ROD ACTING UPON SENSING MEANS TO PRODUCE ANOTHER SET OF ELECTRIC SIGNALS PROPORTIONAL TO ITS DEFLECTION, SAID OTHER SET BEING SUPERIMPOSED ON SAID SET OF SIGNALS SO AS TO REDUCE DEFLECTION ERRORS OF THE TRACER POINT.

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