USRE25648E

USRE25648E - pattern tracer control servosystem

Info

Publication number: USRE25648E
Authority: US
Inventors: Lee Herndon Jr
Original assignee: Pegasus Laboratories Inc
Current assignee: Pegasus Laboratories Inc
Priority date: 1957-07-02
Filing date: 1964-03-19
Publication date: 1964-09-29

Description

Sept. 29, 1,964 1 R. HERNDON, JR Re- 25,648

PATTERN TRACER CONTROL sERvosYsTEM Original Filed July 2, 1957 5 Sheets-Sheet l INVENTOR fR/V0 O/V J'i Sept- 29, 1964 L R. HERNDON, .1R

PATTERN TRACER CONTROL SERVOSYSTEM Sheets-Sheet 2 Original Filed July 2, 1957 wenn #fo/r,

MPl/F/IR Sept. 29, 1964 L R, HERNDON, JR Re. 25,648

y PATTERN TRACER CONTROL SERVOSYSTEM Original Filed July 2, 1957 5 Sheets-Sheet 3 INVENTOR.

LEE R. HER/YDO/Y JR,

4 TTOIVEYS United States Patent Office Re. 25,648 Reissued Sept. 29, 1964 25,648 PATTERN TRACER CNTRL SERVOSYSTEM Lee R. Herndon, Jr., Birmingham, Mich., assigner to Pegasus Laboratories, Inc., Berkley, Mich., a corporation of Michigan Gginal No. 2,983,858, dated May 9, 1961, Ser. No. 669,626, July 2, 1957. Application for reissue Mar. 19, 1964, Ser. No. 366,930

Claims. (Cl. 318-28) Matter enclosed in heavy brackets l appears in the original patent hut forms no part of this reissue speciication; matter printed in italics indicates the additions made by reissue.

This invention pertains to a tracing mechanism and more particularly to a device which has a stylus or probe pivoted in fixed relation to the axis of a cutting tool. The stylus automatically contacts a template which is fixed to a workpiece table and maintains Contact at a constant deilection with said template thereby guiding the cutting tool or, as in the embodiment described below, the workpiece table, so as to form a piece identical with the template. y

This invention utilizes an electrical circuit to move the cutting tool relative to the workpiece table in a direction normal to the deiiection of a deflected probe with corrections rnade to the table, in the opposite direction of the error which is detected by the difference between the actual probe deflection and a given constant reference deflection. If such a difference exists, an electrical signal is sent to a power means which changes the direction of the table movement until the probe deection and the reference deflection are equal.

In this embodiment, the probe is connected to two perpendicularly aligned differential transformers which may be called X and y transformers so that movement of the probe will move one or both of the transformer cores altering their `output in a linear proportion. Likewise the error signal is resolved into signals for perpendicularly aligned power sources for moving the table.

A distinguishing feature of this invention is the means for establishing, transforming, and comparing the probe signal with a reference signal. The differential transformer connected -to the tracer probe has a movable core which, when centered, balances the output of op positely wound secondaries so that the voltage from one secondary will be equal to and opposed the voltage from the other secondary portion. Movement of the core will result in an output of one sign for movement in one direction and of an opposite sign for movement in an opposite direction. The excitation for the y transformer is 90 out of phase with that for the X transformer. This probe output or probe deection voltage is then fed to a dernodulator which is a phase splitting device for reversing every 180 the wave form of a sinusoidal input resulting in a D.C. voltage corresponding to the probe deection and core position. The signal or exciter voltage used to excite the probe transformers is used to demodulate the probe output in the phase splitting circuit. The demodulated signal is compared with a reference signal which is obtained in a similar phase splitting circuit in which the sum of the x and y probe signals is used to demodulate each of the x and y exciter signals which results in wave forms each having an amplitude dependent on a direction of the probe deflection instead of the amount or degree of the probe deflection. By using the sum of the x and y probe voltages to demodulate each exciter voltage, each exciter voltage will be split or reversed at the point where the X, y voltage curve changes direction. The point at which the X, y voltage curve changes direction will vary depending on the value of X relative to y since the X and y voltages are 90 out of phase, and this will cause the x and/ or y exciter voltages to be cut off or reversed twice each cycle with reversal point dependent on the relative Xy values so that the D.C. amplitude will vary according to direction of probe deiiection.

Other features of the invention will become more apparent when explained in connection with the drawings in which:

FIGURE 1 is a schematic circuit diagram of the control mechanism of this invention;

FIGURE 2 is a schematic pictorial view of a probe and two differential transformers;

FIGURE 3 is a Wiring schematic of a single differential transformer;

FIGURE 4 is a wiring diagram of a demodulator; and] FIGURE 5 is a schematic wiring diagram of the resolverL; and

FIGURE 6 is a diagram showing representative wave ,forms for the various voltages developed and employed in the control system.

In FIGURE l is shown in schematic of the control system of this invention wherein sinusoidal exciter voltages are generated at 21 with one voltage differing from another by in phase. These two voltages differing in phase by 90 are sent respectively to x and y

dilferential transformers

22, 23 with each of these transformers having a movable core connected to a tracer probe 24 shown in FIGURE 2. These transformers are connected respectively to x and

y demodulators

26, 27 feeding each demodulator a deflection signal modified by the core and probe position. As shown, the exciter signal for transformer 22 is delivered to demodulator 26 and resolver 28, while the exciter signal for transformer 23 is delivered to demodulator 27 and resolver 28. Modified or deflection signals from

transformers

22 and 23 are also fed to re'- solver 28 which vectorially combines the two signals and uses this vectorial combination to demodulate the y exciter voltage and the x exciter voltage with these demodulated signals shown respectively across the

resistances

31, 32.

Looking momentarily at FIGURE 2 is seen template 33 which in this embodiment is fastened to a milling machine table and moves with the table so that probe 24 has a normal deflection of constant magnitude. The workpiece, not shown, is also connected to the moving table while probe pivot 34 and the cutting tool, not shown, remain in fixed relation to one another and to the milling machine frame. Of course, the probe and cutter could be moved while the template or pattern and the workpiece were stationary. In this device, the template is moved with a tangentialvelocity to probe 24.

As seen in FIGURE 2, there is connection between probe 24 and each of the cores of

transformers

22, 23 so that a movement of probe 24 about pivot 34 will move one or both of the cores. In FIGURE 3 a schematic diagram of a singie transformer is shown with movable core 36 primary winding 37 and secondary windings 38, 39. As shown the secondary windings oppose one another so that with a centered core the output across the secondary terminais will be zero. However, if the core is moved to the right or left, there will be an output across the secondary.

Shown in FIGURE 4 is a wiring diagram of a demodulator two of which are located in the resolver of FIGURE 5 and two of which are located at 26, 27 in the diagram ol FIGURE l. The operation of these demodulators is simi lar in nature as is their construction with the exception that the

demodulators

65, 66 of the resolver 28 each provide two output voltages of opposite polarity. Trans former 42 has primary winding 43 and

secondary windings

44, 45, 46 and 47, each of which is connected in eries with a resistance between the grids and cathodes of tiodes 5-1, 52; 53 and- 54, respectively. It isseen thatJ lith a wave form of one direction induced into the secndary winding which makes the grid end of winding 4' more positive thanthat of 45', tubes 51 and 54 will re. since their grids. are respectively positive relative their cathodes. A wave form-inducedA in an opposite irectionwill.- cause tubes-,52,A and 53jtore. With tubes 1 and 54 tiring, the signal induced in the upper half of acondary 4010i ar transformer. 41 will have one conarmation which willbe coupledbetween line 61' and line 2, while if

tubes

52 and 53 lire; the inverted signal from ie. bottom halff of secondary 40will1be-co-upled between

nes

61 and 62. Therefore, by reversing the direction of ie. currentz inL primary 43 the wave form selected from :condary 40 can be inverted, with this wave form apearing inline 611, and line 62; Asshown in a resolver iagram FIG. 5, the voltage between lines 61'V and 62 is lteredY to obtain. the average DC.. component.

The resolver 28 is shown schematically in FIGURE 5. and y. exciter signals appear. at the primaries of. transrmers 41 of

demodulators

65, 66. The modified exciter r dellection signals fromthe

probe transformers

22, 23 te. combinedv at. potentiometer 67' which is tapped into nplilier 68 which amplifies the sum of the wave forms pparing at 69', 70 .andi applies this sum to the primaries E transformers 42.

of'demodulators

65, 66.. Switch 97 provided and if opened, breaks the circuit to the pritaries of transformers 41f causing. the probe, and cutting iol, to break contact with the template and workpiece. his is advantageous since the work may be stopped at 1y point inthe cycle. The output or demodulated sigils in lines 61, 621 are converted to their. average D.C. tlues by. being fedrespectively through compensating

ltcrs

72, 73 to center tapped grounded resistors 98, l and then to the gridsv of cathode follower circuits 7.4; 5. with-the outputs in lines 611, 62 appearing across oposite endsk of center tapped

resistances

31, 32 for the and X. coordinates, respectively, as-.shownin-.FIGURE l; These two resolver outputs. are reference voltages and ave a. dual'function. Their negative values are reference :llection signals whichappear for the X coordinate at :sistance 78'- and for they coordinate at resistance 79. he positive-value of one output andthe negative value the other output, when applied to the control of the vble drive for. the other. coordinate, are feed signals hich control the relative rate of movement between the -obe andtemplate, andthence, between the tool andthe ork, in aV direction always normalv to the direction of 'che deflection. Accordingly, the positive value of the resolver output, atresistance 31, is supplied to resistance 5in the control system for the X coordinate drive; and, @negative value ofthe X resolver. output from resistance 5 is suppliedto resistance 96m the y coordinate control stem.

Resistances- 31 and 32 form part of. a gang potentineter, as shown in FIGURE l, so that the feed signals, ld hence the feed rate, can-be easily varied from zero maximum.

Looking again at FIGUREI l it is seen that the outputs actualv deflection signals of X and

y demodulators

26, 27 pear respectively across resistances 76, 7-'7 which re- ;tances are connected respectively to

resistances

78, 79 lrosswhich appear the X and' y reference deilection sigtls. The-Sum of theplus voltage across resistor 76 and e minus voltage across resistor 78 is the X. dellection ror voltage. Likewise, the sum of the plus voltage ross resistor 77' and the minus voltage across resistor Pis the y deflection error voltage.

These X- and y de flectionerrorvoltages are respectively .ssed through

resistances

80 and 81 and appear at sistance 93 for the X coordinate control system and sistance 94 for the y coordinate control system, these stems respectively including

amplifiers

82, 83 which gulate the

servo valves

84, 85 and hydraulic motors 86,

i 87. Tachometers S8, 89 record respectively the speed of the milling-table in the X- and y directions. These speeds each rellect the sum of the rate of feed and any error on each coordinate and hence the tachonieter outputs indicate these sums as X andy negative feedback potentials across resistances 91 and 92 respectively.

As a result, each coordinate drive means is actuated in response to the sum ofthe error signal, the feed signal and the negative feedback potential. lf desired a third transformer 1.61 may be placed in a plane perpendicular to the plane formed by the

transformers

22, 23 and connected to an exciter demodulator 162 and in turn to amplier 163, sewo valve 104, and cylinder which operates the milling head to provide a three dimensional automatically controlled unit.

OPERATION Representative wave forms for the various voltages developed and' employed in the control system are shown in FIG. 6, illustrating a normal condition in which the probe deflection is equal to the reference deflection. The probe is always deflected along a line substantially normal to the line of tangency at the-contact point between the probe 24 andthe template 33, and the reference deflection, in direction and amount, is employed to obtain a normal feed signal for driving the machine table in a direction 90 to the direction of deflection.

Referring to FIG. 6 and to the overall circuit diagram, FIG. l, the eXcitor 21 supplies a sinusoidal X-eXcitation voltage tothe transformer 22 and a sinusoidal yexcitation voltage 112 to the transformer 23, the y-excitation being 90 out of phase with the X-eXcitation. X and y

probe output voltages

114 and 116` are developed by the-transformers 22 and 23y depending upon the position of their respective cores as determined by the position of the probe 24. The

probe output voltages

114 and 116 illustrated in FIG; 6 represent an instantaneous condition, it being understood-that these voltages will each vary with probe position as the probe moves around the-template.

These X and y probe output' voltages are respectively fed to the terminals 24= and 25 of the resolver 28. Referring to FIG. 5, the vectorial sum of the X and y probe output voltages appears across resistance 67 and is illustrated by the representative Wave form 11S in FIG. 6. This wave form is displaced from the output voltage waves 1-14- and 116 by an angle 6 which represents the direction of deilection of the probe center relative to the X axis. Voltage 118 is squared to the form represented by the wave 120 in FIG. 6 inthe ampliiier 68 and is supplied to the input terminal 5i) (FIG. 4) of each of the demodulatorsy 65- and 66 of the resolver. The X and

y excitation voltages

110 and 112 are supplied respectively to

terminals

29 and 30 of the resolver demodulators (which correspond to the other dernodulator input terminalk 51) (FIG. 4), and these voltages are each demodulated by the voltage 120 to obtain an X-reference voltage 122 and a y-reference voltage 124. Each of these

voltages

122 and 124 are filtered, as previously described, to obtain X and y D.C. reference voltages 123 and 1125 respectively. These D.C. reference voltages appear at

resistances

32 and 31 for the X and y coordinates respectively.

rl'ne X probe output voltage 114 is supplied to demodulator Zwhcre it is demodulated by the X-eXcitation voltage 110 to` give the wave form 126 which is filtered to obtain its average D C. value 127, or X. probe deflection signal. This X probe deflection signal appears at resistance 76. Similarly, the y probe output signal is demoduiated and filtered to give the respectiveV y

probe deilection voltages

128 and 129, with the D.C. voltage 12g-appearing ett-resistance 77.

Thev negative value of the X reference voltage 123. appears across resistance 7S andl is confined with the X probel deflection voltage 127 at resistance Sii; the negative value of the y reference voltage is` combined with the y probe deflection voltage at resistance 81. If the actual deflection as measured by the

probe output voltages

114 and 116 is equal to the reference voltages, the net signal at the

resistances

80 and 81 will be zero in each case, or in other words, any signal appearing at these resistances will indicate any difference between the actual probe deflection and the reference deflection.

The reference voltages 123 and 125 have values which reflect the angle of the probe deflection relative to the x coordinate which angle is equal to the angle of feed less 90. Consequently, when the positive value of one of these voltages is supplied to the table drive for the opposite coordinate as is the positive value of voltage 125 to resistance 95 for the X coordinate drive, and the negative value of the other vo-ltage supplied to the drive for the other coordinate as is the x reference voltage 123 to resistance 96 for the y coordinate drive, the result is to supply driving signals which reflect the feed angle. The value of these signals and hence the feed rate can be adjusted by the gang potentiometer [38]. Feed can be interrupted by the switch 77 (FIG. 5) and the tool will move away from the work by the amount of the reference deflection.

The outputs of the x and y coo-rdinate tachometers 88 and 89 are adjusted to values slightly less than these feed signals at

resistances

95 and 96 and as a result a much better response is obtained from the system. A small degree of change in the tachometer signal will result in a large degree of change in the net input signal to either of the

amplifiers

82 or 83. This tachometer feed-back loop will be recognized as a means o-f making an accurate variable speed drive for electric as well as the hydraulic driving components illustrated.

It will be appreciated by those skilled in the art that compensation can readily be applied to any of the D C. signals in the control system. By means of such compensation the dynamic characteristics of the control system can readily be changed to adapt it for use with machines of different size, operating speeds, etc.

While preferred embodiments have been described above in detail, it will be understood that numerous modifications might be resorted to Without departing from the scope of my invention as defined in the following claims.

I claim:

1. A system for controlling relative movement between a tracer probe and a template, including drive means operable along first and second angularly related lines of reference, comprising means for supplying a pair of A.C. excitation voltages differing in phase by the angle between said lines of reference, means operable by said probe for producing a pair of probe output signals from said excitation voltages, each of said A.C. probe output voltages being proportional to the magnitude of probe deflection along one of said lines of reference, means for converting each of said A C. probe output signals to a D.C. probe deflection signal, means for obtaining the vectorial sum of said A.C. probe output signals, means for demodulating each of said excitation voltages with the said vectorial sum of said probe output signals to obtain a D.C. reference voltage for each of said lines of reference, means for combining each of said D.C. probe deflection signals with the negative value of the said D.C. reference voltage for the -corresponding line of reference to obtain a pair of D.C. deflection error voltages, means for obtaining a D.C. feed voltage for each of said lines of reference from the said reference voltage for the other line of reference, one of said feed voltages being obtained from the negative value of the other reference voltage, means for actuating said drive means on each line of reference in response to the sum of said D.C. feed and error voltages for each line of reference, and means for comparing the sum of said feed and error voltages with a D.C. feedback voltage proportional to the velocity of said drive means.

2. A control system according to claim l further characterized by adjustable means for controlling the value of said feed signals whereby the rate of feed between said probe and said template can be varied.

3. A control system according to claim l further characterized by said means for demodulating each of said excitation voltages with the said vectorial sum of said probe output signals including circuit means for obtaining said reference voltages in positive and negative values.

4. A control system according to claim 3 wherein said circuit means further includes a compensating network for adjusting at least one of said positive and negative reference voltage values.

5. A control system according to claim 1 wherein said means for converting each of said probe output signals to a D.C. probe deflection signal includes an input voltage derived from the excitation voltage for the corresponding line of reference.

6. vA system for controlling relative movement between a tracer probe and a template, including vdrive means op erable along rectangular coordinates, comprising means for supplying a pair of excitation voltages having a relative phase angle of means operable by said probe for modifying each of said excitation voltages to produce a pair of probe output signals, each of said probe output signals being proportional to the magnitude of probe deflection along one of said coordinates, circuit means for each of said coordinates for converting each of said probe output signals to Va uni-directional deflection signal, a resolver network, said resolver network` including means for vectorially adding said probe output signals and circuit means for each of said coordinates for demodulating the corresponding exciter voltage for such coordinate with said vectorial sum to obtain a unidirectional reference voltage in the positive and negative value thereof, means for comparing the negative value of said reference voltage with the corresponding coordinate probe deflection signal to obtain an error voltage, circuit means for obtaining a feed signal for each coordinate from said reference voltages, said circuit means including a connection to the said positive value of the reference voltage for one coordinate and the said negative value of the reference voltage for the other coordinate, said feed signals being applied to the drive means for the coordinate opposite to the coordinate of the reference voltage from which they were derived, and means for obtaining a feedback voltage from each drive means and comparing such feedback voltage with the sum of the said error and feed signals for each coordinate.

7. In a system for controlling relative movement between a tracer probe and a template and including drive means operable along at least two angularly related lines of reference, means for obtaining signals proportional to the magnitude of probe deflection along said lines of reference, said deflection signals having a relative phase angle equal to the angle between said lines of reference, circuit means for obtaining a feed signal for each line of reference, said feed signal circuit means including means for obtaining the vectorial sum of said deflection signals, means for supplying input signals to said feed signal circuit means, each of said input signals having a phase corresponding to the phase of one of said deilection signals, means for modulating each of said input signals with the said vectorial sum of said deflection signals to obtain a unidirectional reference signal, means for applying each of said reference signals to the control means for the other line of reference as a feed signal and means for reversing the polarity of one of said feed signals.

8. Control circuit means according to claim 7 further characterized by means for selectively compensating said feed signals.

9. Control circuit means according to claim 7 further characterized by means for varying the amplitude of each of said feed signals.

7 10. Control circuit means accordingto claim 7 further characterized by said cifcuitmeans including meansl for obtaining saidA reference signals in positive and? negative values and means for employing the said negative` values thereof as referencedeection signals.

Branson Dec. 27, 1949 Berry et a1. Feb. 28', 1950 Hill, W. R.:

8 Wetzel June 20, 195() Fyklund et a1 July 3, 1951 CalosiY Jan. 27, 1953 Warsler Mar'. 24, 1953 Berry May 25', 1954 Johnson etal. Dec. 18, 1956 StokesV June 3, 1958 OTHER REFERENCES Electronics'in Engineering, McGraw-Hill,

NY., 1949,V pp. 246-247, FIGS; 15S-15.9;