US3704372A

US3704372A - Optical pattern tracer

Info

Publication number: US3704372A
Application number: US81784A
Authority: US
Inventors: Robert E Parker; Malcolm A Lodge; George S Jewell
Original assignee: Westinghouse Canada Inc
Current assignee: Westinghouse Canada Inc
Priority date: 1969-10-20
Filing date: 1970-10-19
Publication date: 1972-11-28
Anticipated expiration: 1989-11-28
Also published as: DE2051528A1; FR2066165A5; JPS4916916B1; CA917773A; NL7015326A; DE2051528C2; GB1292507A; CH531395A

Abstract

A rotary scan line/edge tracer using a motor driven mirror to produce the rotary scan. The motor also drives a generator for providing two coordinate reference signals. The mirrors assembly is exchangeable to provide varying scan diameters. The photocell is mounted adjacent the center of the focusing lens at the lower part of the apparatus, thus permitting a coaxial arrangement of the motor and mirror and lens producing a compact assembly. The reference signals are sampled instantaneously to produce coordinate drive signals.

Description

United States Patent Parkeretaly 1 i541 OPTICAL PATTERN TRACER Jewell, Ancaster, Ontario, all of' Canada [73] Assignee: Canadian Westinghouse Company Limited, Hamilton, Ontario, Canada 22 Filed: Oct. 19,1970 211 Appl .No.:81,784

3o Application Priority n w Oct. 20, 1969 Canada ..065212 52 U.S.Cl. ..250/202, 250/235, 250/236, 350/99 51 Int. Cl. ..G05b1/00 [58] FieldolSearch ..250/202, 203, 234, 2 35, 236; 350/26, 99

[56] References Cited UNITED STATES PATENTS, 3,395,282 7/1968 Blackwell ..250/202 1 51 Nov. 28, 1972 6/1963 Wills ..250/202 2,997,598 8/1961 Gramrn ..250/236 3,496,437 2/ 1970 Layden ..250/202 3,135,904 6/1964 PurIthiser ..250/202 3,017,552 1/ 1962 Brouwer ..250/202 3,004,166 10/ 1961 Greene ..250/202 3,322,952 5/1967 Jewell ..250/202 Brouwer ..250/202 Primary Examiner-James W. Lawrence Assistant Examiner-D. C. Nelms Attorney-R. H. Fox

are sampled instantaneously to produce coordinate drive signals.

2Clains,l2DrawingFigures PATENTEnuuv28 1912 3. 704.372

sum

02 or 12 SAMPLE L AND HOLD SPEED PATENTEHNUY28 I972 3,704,372 sum 03 0F 1 POWER SUPPLY NEUTRAL PATENTED Nov 2 8 I972 SHEET on or 1 PATENTEuN0v 28 m2 3. 704,372

SHEET 05 HF 1 HIGH SPEED g E TRAVHTRACE q E 5 4 DIRECTION POWER DRIVE TRAVERSE PATTERN POWER DRIVE L r J FIG. 3

PATENTEDuuvze I972 SHEET 070F 12 n20 FEE 2O WWW QOP V MOP M i P .Q.%

n? OK ":0 BOP PATENTED NOV 28 I972 SHEET 08 0F 1 v GE Ommmm+ V PATENTEU um 28 m2 SHEET 10 0F 12 M 0.6% or O mI 02655.

PATENTEDNHY 9 3. 704,372

SHEET 11 [1F 12 J 42\ I ,164 F HIGH TRAVERSE STEER SPEED TRACE STRAIGHT CUT FIG. 4f

PATENTEDnuvze I972 PHOTOTRANSISTOR OUTPUT (80) a SIGNAL OUTPUT SINE OUTPUT COSI NE OUTPUT d COMPARATOR OUTPUT (97) SAMPLE PULSE OUTPUT (101) FIG. 5

3.704.372 SHEET 12 [IF 12 +o-o5ov 0 W V T! 1.0V LEVEL(86) THIFEEVSSLOLD II+-- I- LJL iIIA/WMWL OPTICAL PATTERN TRACER This invention relates to optical pattern tracing controls and in particular, to controls of the type which repetitively scan the pattern to be followed in a circular manner, derive a signal from such scanning operation and utilize the signal to control coordinate drive mtors. I

There are various types of optical pattern tracing machine control systems including scanning and nonscanning tracing heads, friction and coordinate drive machines, edge and line tracers. This invention has particular application to a pattern tracer of the circular scanning type for operation with a coordinate drive system which may be used for either line or edge trac- By a circular scanning tracer is meant a tracer which views the pattern in such a manner that the point observed by the tracing head is caused to rotate repetitively so as to describe'a circular path on the surface bearing the pattern when the head is stationary. Naturally, when the head is in translational motion, the point scanned by the tracing head will more closely approach an epicycle.

The detector in the tracing head is arranged to produce a signal indicative of a change in illumination of the detector. In this way, the device may operate either as a line tracer, i.e., a tracer of a narrow mark on a surface area, or as an edge tracer, i.e., a tracer of the transition from a reflective to a less reflective area as in the case when the pattern is a silhouette. The signal representing this transition is then processed and used to control a pair of motors which when associated with suitable machinery, will cause the tracing head and related machine tool to more in a plane in accordance with the pattern as controlled by the motors.

It will be appreciated that in accordance with general practice in this field, the convolutions performed by the tracing head will be similarly performed by the machine tool which may, for example, be a cutting torch and in this way, the material to be cut will be shaped into the same form as the pattern being traced by the tracing head.

In circular scanning tracing heads the diameter of the circle described by the optically sensitive area as it effectively scans the pattern establishes the lead" of the scanner. Lead, a term in common use in the art, determines the relationship between the steering axis of the tracing head and the point on the pattern being sensed. As will be appreciated, in order for a tracer to respond to deviations in the pattern, information relating to such deviations must be received in the control system before the tracing head has left the pattern, otherwise the tracer will have left the pattern before compensating action can be introduced. it will appear, therefore, that the lead of the system may vary depending on the tracing velocity, the higher the velocity the greater the lead necessary, assuming other factors in this system remain constant. It will be seen then, that for any given system a certain minimum lead will be required for a given tracing velocity. On the other hand, it is well known and understood that as the diameter of the scanning circle becomes larger, the discrimination becomes less and the accuracy of tracing is reduced. Therefore, for precision, the diameter of the circle must be kept to a minimum.

With these two opposing factors, it will be evident that changes in tracing velocity will produce changes in the minimum necessary diameter of the scanning circle and for the ultimate precision, this diameter should be adjustable. In order to produce such adjustable diameter, the tracing head of the present invention provides exchangeable elements which vary the scanning diameter.

A machine tool, in most cases actually removes a portion of the material when making a cut. In the case of the gas cutting torch the width of the cut is referred to as the kerf. In order that the piece cut from the material shall be the same size as the pattern it is necessary to make compensation for this kerf; The tracing head of the present invention is arranged to be conveniently adjusted to compensate for removed material be producing apparent displacement of the pattern in a direction such as to correct for the kerf in an amount selected at will by the'operator.

In order to provide the desired control a signal is derived from the tracing head and applied to an electronic circuit which accurately selects the transition from one condition of reflectivity to another condition of reflectivity of the pattern, converts the signal to a suitable form for further processing, and in co-operation with certain other signals from the tracing head which are phase-related to the rotational position of the scan, produces a pair of coordinate signals, i.e., an X signal and a Y signal, which are then used to control coordinate drive motors.

A clearer understanding of this invention may be had by a consideration of the following specification and drawing, in which:

FIGS. la, lb and 1c together, show a schematic diagram of a tracer system in accordance with this invention;

FIG. 2 is an elevational view, partially in section, of a tracing head for use in the system;

FIG. 3 is a view of a control panel showing the location of the various controls for the system;

FIGS. 4A to 4F are schematic diagrams showing the circuit details of certain portions dramas masses in the schematic diagram;

FIG. 5 is a series of wave form diagrams useful in an explanation of the operation of the system.

Considering now the schematic diagram shown In FIGS. la, lb and 1c, it will be seen that lamps 6 illuminate a drawing 7 and the light from a certain portion of the drawing is focused through the lens 8 and reflected by the mirror 9 onto a photocell 10. The mirror 9 is driven by the synchronous motor 11, in such a manner that the area of the drawing scanned by the optical system moves in a circular path. Also on the shaft of motor 11 is a timing generator consisting of a permanent magnet 12 and a pair of stator windings l3 and 14 arranged physically at right angles to each other so as to produce two sine waves at right angles to one another or in effect, a sine wave and a cosine wave.

These signals, together with the signal from photocell 10, are applied to preamplifier 15. The polarity of the sine and cosine wave applied to the preamplifier is selectably reversable by means of the contacts of relay 16. Two outputs from the preamplifier, the first being the signal as amplified, and the other being a signal representative of one half the maximum deviation of the signal, are both applied to the logic circuit 17.

. One output from the logic circuit consists of a pulse indicative of the time when the signal traverses a certain level, this timing pulse is used to define the edge of the pattern. Another signal is produced which is indicative of the presence of a pattern to be followed and this signal is applied to the on-pattem relay 18 through the contacts of the light control relay 19.

The pulse output from the logic circuit is applied together with the cosine and sine output from the preamplifier to a sample-and-holdcircuit 20. This sample-and-hold circuit produces a pair of signals, one representative of the value of the sine wave at time of occurrence of the pulse from the logic circuit, and the other signal representative of the value of the cosine wave at the instant of occurrence of the pulse from the logic circuit. As will be seen, these two signals represent the necessary X and Y coordinate velocities in order to maintain the tracing head over the pattern.

These X and Y coordinate signals are applied through the contacts of mode relay 21 and speed control rheostat 22 to the traverse control circuit 23. A pair of reference voltages of equal positive and negative value are also produced inthe sample-and-hold circuit and may be substituted for the X and Y coordinate signals in which case these signals are then applied to the traverse control circuit 23. The X and Y coordinate signals are then passed through the traverse control circuit and on to their respective servo amplifiers, X servo amplifier 24 and Y servo amplifier 25. The outputs from these servo amplifiers are applied to a pair of power amplifiers, the x-power amplifier being generally designated 27 and the y-power amplifier being generally designated 28.

The output from the amplifiers is applied through

relays

29 and 30 to the X motor 31 and the Y motor 32. Each of these motors has on its shaft a tachometer generator, the X tachometer being designated 33 and the Y tachometer being designated 34. The outputs from these tachometer generators are fed back to their respective servo amplifiers through the traverse control.

The necessary DC potentials for operating the electronic circuitry are derived from power supply 35 which is provided with alternating current supply, for example, 115 volts 60 cycles through the contacts of relay 36. i a

The tracer is controlled by the operator from a control panel shown in the dotted outline in the lower por tion of FIG. 1 and designated 37 containing the control switches for controlling the various functions. For example, control switch 38 controls the operation of relay 36 through which primary power is applied to the equipment. Control switch 39 controls relays 29 and 30 through which the power amplifiers are connected to their coordinate drive motors. Switch 40 controls the light relay 19 which selectively energizes either the flood lamps 6 or the indicator lights 64. Switch 41 controls the direction of rotation of motor 11 and also the actuation of the direction relay 16 which, as previously previously indicated, may control the phase of the sine waves applied to the preamplifier. Switch 42 controls the priority of the four position direction switch 26 to permit straight line cutting without a pattern or altematively automatic line acquisition. In its reverse direction it is a momentary contact switch to permit jogging of the apparatus to assist in line acquisition. Switch 43 controls the value of the speed signal applied to the direction switch 26 and also controls the mode relay 21 to open the tachometer circuits during high speed operation. Associated with the various switches are, when applicable, various lamps which indicate the condition of the switch or the system for the information of the operator.

Considering now FlG. 2, this shows an elevation of the tracing head including the elementsshown in the dotted outline to the left of FIG. I and bearing the general designation 45. As will be seen, the flood lights 6 provide illumination to the pattern 7 and the light from he pattern 7 is received by lens 8 and directed towards the mirror 9, and back on to the photocell 10. The photocell 10 is mounted directlyv over the center of the lens 8 and here, while it slightly'reduces the aperture of the lens, it has no effect on the focus of the image from the pattern 7. The mirror 9 is mounted in a mirror carrier 46 mounted in the end of a quill 47 which is fixed to the shaft of motor 11 by means of a set screw 48. Also mounted within the quill is the permanent magnet 12 and centered about the quill are the

stator windings

13 and 14 wound on suitable

laminated stators

49 and 50.

It will be noted that these stators together with the motor 11 are mounted in a sub-frame which may be rotated in the main housing 52. A cap 53 covers motor 11 and is fixed to the sub-frame 51. Suitable graduations and indicia are provided at 54 to indicate the relative rotational position of the sub-frame 51 and the main enclosure 52. The necessary electrical connections from the motor 11, the stators l3 and 14, the photocell 10, the lamps 6 are provided through an electrical connector 55. It will be noted that the electrical connections to the sub-frame 51 pass through a disconnectable plug and socket 56 so that the sub-frame may be completely removed from'the general enclosure as desired. One reason for making the sub-frame removable is to enable the operator to replace the mirror assembly mounting 46. it will be seen that the mirror 9 is offset and at an angle to the axis of rotation of motor 11. This angular relationship produces the desired circular scan and the degree of angularity determines the diameter of scan. By substituting various mirror assemblies, the operator can select the desired scan diameter for reasons previously indicated.

Considering now FIG. 3, it will be seen that the various controls and indicator lights from the control unit are arranged in a single panel for the convenience of the operator, and include the lights switch 40, the tracer switch 41, the speed control rheostat 22, the power and drive

switches

38 and 39, the high speed push-button 43, the direction control switch 26 and the traverse and trace control switch 42. Also included are indicator lights, a first light 60 to indicate that power is on, a second light 61 to indicate that the drive is on, a third light 62 to indicate when the machine is in the traverse mode, and a fourth light 63 to indicate when the machine is in receipt of a signal indicative of a pattern, that is, when the on-pattern relay is energized.

OPERATION The operation of this system will now be described in association with the foregoing figures, and in addition, FIGS. 4A to 4B and 5.

To start up the apparatus, the operator turns on power switch 38 thus energizing the relay 36 which provides the necessary supply voltage to the power supply. He then switches on drive switch 39 which energizes relays 29 and 30 thus enabling the

motors

31 and 32 to be driven by their related power amplifiers. At this point, the indicator lights 64 are energized, these lights are not shown in FIG. 2 since they are out of the plane of the section, but are arranged around the lower part of the tracing head so as to project a circle of light immediately under lens 8 which approximately defines thetracing circle. The operator may now put the switch 42 in the traverse position thus illuminating traverse light 62 and providing a potential to the contacts of direction switch 26. By manipulation of direction switch 26 any one or two of the contacts may be closed, thus causing the various relays in the traverse control shown in FIG. 4D to be operated. For example if the direction switch is moved in the +Y direction the relay 70 is energized, opening the normally closed contacts 70-1 and closing the normally open contacts 70-2, thus applying the potential from terminal74, which is the +speed signal which has been derived from the sample-and-hold circuit, through the contacts of mode relay 21 and the speed control 22 to the traverse unit 23, thus to terminal 74, through the normally closed contacts 71-1, 72-1 and 73-1 to the ysignal terminal 75. In a similar way, operation of the X contact in the direction switch 26 will actuate relay 71 opening normally closed relay contact 71-3 and closing normally open contact 71-4 thus applying the potential from terminal 74 through contact 71-4, 72-3, 73-3 to terminal 76. The Y contact of the direction switch operates relay 72 and the -X contact operates relay 73 both of which function to provide negative signals to the

same terminals

75 and 76 from the negative supply on terminal 77 which is derived from the sample-andhold circuit in a manner similar to the potential supplied on terminal 74.

It will be noted that actuation of

relay

70 or 72 opens circuits contact 70-6 or 72-6, and closes contact 70-5 or 72-5. This provides a return path for the drive relays 29 and 30 to ground without going through the contacts of the on-pattern relay. In a similar manner, actuation of

relay

71 and 73 provides a return path for relay 29 to ground without going through the on-pattern relay.

The operation of the direction. switch, therefore, has applied suitable voltages to

terminals

75 and 76 which are then applied to the

servo amplifiers

24 and 25, and through the

power amplifiers

27 and 28 and relays 29 and 30 to the

drive motors

31, 32 causing these motors to rotate with a speed determined by the voltage at

terminals

74 and 77, and with a direction determined by the selection of the relay or the direction of closure of direction switch 26. In this way, the operator can maneuver the device until the spot of light produced by the indicator lamps 64 is over the pattern. At this time, the operator may close the tracer switch 41 in a direction to provide the direction of tracing desired as shown by the arrow on the control unit causing the tracer to trace clockwise or counterclockwise around the outside of the pattern. I

The closing of tracer switch 41 energizes the motor 11 in one direction or the other, causing it to rotate either clockwise or counterclockwise and also, may or may not energize relay 16 which operates as a reversing switch to reverse the outputs applied from the sine and

cosine generators

13 and 14 before applying them to the preamplifier 15.

Assuming that the operator has located the tracing head over the pattern by means of the direction switch and the motor is rotating in a suitable direction, the mirror is rotated thereby and causes the illumination from a portion of the paper including the pattern to be reflected on to the photocell 10. As the photocell 10 crosses a transition between a light and a dark area, a signal is produced and applied to the preamplifier. If the pattern being traced is a line, the signal produced by the photo transistor 10 will be of the general form shown at a in FIG. 5. This signal is applied to terminal of the circuit shown in FIG. 4A and through a suitable shaping network to operational amplifier 81 which is provided with suitable potentials as shown, derived from the power supply, and the output from the amplifier appearsat terminal 82 as shown at b in FIG. 5. This output is also supplied to the circuit comprising transistors 83 and 84, which are arranged as peak-topeak detectors so that the output from the emitters of these two transistors represents the peak-to-peak value of the signal.

This value, which is a substantially constant voltage which varies onlywith variations in illumination or contrast of the pattern, is applied to operational amplifier 85 which is so arranged that the output from the amplifier, which appears at terminal 86, is maintained at a value representative of the median value of the peakto-peak signal. This DC signal at terminal 86 is fed back to amplifier 81 to restore the DC level of the signal and maintain it such that deviations are equal about a reference zero-axis.

The outputs from the sine and cosine generators shown at c and d in FIG. 5 are also applied to the preamplifier through the contacts of relay 16, as previously indicated. These sinusoidal waves are applied to operational amplifiers 87 and 88 which are arranged to stabilize the value of the sine waves. The output from operation amplifier 87 is applied to a buffer amplifier consisting of transistors 89 and 90, and the output applied to terminal 9. In a similar manner, the output from operational amplifier 88 is applied to buffer amplifier consisting of

transistors

92 and 93 and appears on terminal 94.

The level signal from terminal 86 and the photocell signal from terminal 82 are applied to the logic circuit 17, which is shown in greater detail in FIG. 4b. As will be seen, these signals are applied to differential comparator 97 which is so arranged that if a signal on terminal 82 exceeds the DC level on terminal 86 by a predetermined amount, a negative voltage step is produced as shown at e in FIG. 5. This step persists as long as the signal at b exceeds the predetermined value as indicated by the dotted line. This voltage is coupled through capacitor 98 to the monostable circuit consisting of

transistors

99 and 100.

This monostable circuit is so arranged that transistor 99 is normally conducting and transistor 100 is normally cut off. On receipt of the negative impulse through capacitor 98, transistor 99 is switched off, thus switching on transistor 100. The monostable circuit 7 y then returns to its normal stable condition in a time determined by he value of resistor 150 and capacitor 151, producing an output of the form shown at f in FIG. on terminal 101. I

1 An impulse is also coupled from the collector of transistor 99 through capacitor '102- to a second monostable circuit consisting of

transistors

103 and 104. Transistor 103 is normally switched on, but the trailing edge of the pulse on the collector of transistor 99 being a negative going front, switches off transistor 103, thus'switching on transistor 104 by virtueof the coupling through the buffer amplifier consisting of

transistors

105 and 106 which are coupled to the base of transistor 104. This circuit remains in this condition withtransistor 103 out off for a time determined by the value of capacitor 152 and resistor 153 primarily. The resultant pulse is applied to the base of transistor I07, and also to thebase of transistor I08 and has a form as shown mg in FIG. 5. I

For the sakeof clarity there is shown at h in FIG. 5 a schematic view of a pattern consisting of a line, shown shaded, a scanning circle, having a radius designated lead, and the' effective viewing area of the photo transistor designated aperture. As the aperture passes over the pattern it produces the impulse shown at a in FIG. 5, which in turn gives rise to the pulse shown at g in FIG. 5. This pulse has a duration as indicated at h in FIG. 5 as the inhibit period and equal to approximately the time of 516th of one revolution of the scan. The period between the end of the inhibit period and commencement of the next inhibit period is referred to as a window, and it is only during the window period that signals from the photo transistor can produce sample output pulses for reasons as will now appear.

As long as transistor 103 is cut off, transistor 107 is turned on and prevents transistor 100 from being turned on even though transistor 99 receives an output from a comparitor. However, as soon as the inhibit period ends and transistor 103 once more becomes conducting, transistor 107 becomes non-conductive and when transistor 99 receives the next comparitor pulse and is cut off, transistor I00 becomes-conductive changing the circuit to its. unstable condition and producing a sample pulse output at terminal 101.

In this way, signals occurring at times other than the preferred time,'that is, during the window, which is equivalent to saying at periods other than the inhibit period, cannot produce a sample pulse, because transistor 100 cannot be turned on, and transistor 103 cannot have any effect on the inhibit period because it is already switched off and only negative pulses can be applied to its base from the collector of transistor 99.

The pulses as shown at g in FIG. '5 are also applied to the base of transistor 108 as was previously indicated. This transistor together with transistor 109 operate as a darlington pair and produce a potential on capacitor 110. This circuit is arranged so that a potential of a suitable level to maintain on-pattern relay l8 energized is developed as long as pulses are being received on the base of transistor 107. Capacitor 110 provides a suitable storage device to ensure that the relay holds in through the intervening periods and permits a slight delay in acquisition of the pattern. This output appears at terminal 111, and is applied through the contacts of relay 19 to the on-pattern relay 18.

The pulse output from terminal 101 and the sine and cosine output from the

preamplifier terminals

91 and 94 are all applied to the sample-and-hold circuit 20, shown in more detail in FIG. 4c. The pulses on terminal 101 are applied to a shaping

circuit including transistors

112 and 113, which produce, from the pulse, a suitable sampling pulse having a duration of 60 microseconds. This sample pulse is applied to the gates of a pair of FET transistors I14 and 115. To the input of transistor 115 is applied a sine wave from terminal 91. To the input of transistor 114 is applied the output from the differential amplifier. If there is any difference in these two signals during the gating period, it is'amplified by the amplifier 116 and the output from the amplifier adjusted to maintain the voltage at the last sample level. This value is then applied to operational amplifier 117 and through the buffer amplifier consisting of

amplifiers

118 and 119, to the output terminal 120. In a similar manner, the sampled value of the cosine wave appearing at terminal 94 is stored in the sample-and-hold circuit and appears at terminal 121.

As will be seen from FIG. 4d already considered, the potentials on

terminals

120 and 121 will be applied to the X signal terminal 76 and the Y signal terminal 75 in the absence of operation of any of the

realsy

70, 71,72 of 73. Considering the signal on terminal 76, this is applied to servo amplifier 24. A further signal from the tacho generator 33 is applied through the traverse circuit 23 from terminal 22 (FIG. 4b) through the contacts of relay 123 to the terminal 124 and thence, to the servo amplifier 24. As will be seen in. FIG. 4e, these signals are applied to an operational amplifier 125 with suitable feedback and correlation of the signals to provide a maximum gain with adequate stability. The DC signal thus produced is applied to a buffer amplifier consisting of transistors 127 and 128 and transistors 129, 130, 131 to provide a suitable drive signal for power amplifier '27 which provides a reversible DC supply to motor 31.

In a similar manner power amplifier 28 provides a reversible DC supply to motor 32, as has been explained. The amplitude and polarity of the DC signal applied to the X and

Y motors

31 and 32 respectively is a function of the value of the sinusoid at the instant of occurrence of the sampling pulse as illustrated in FIG. 5. The speed of rotation of the X and Y motors therefore is proportional to the direction of the line eitpressed as co-ordinate values on an X and Y co-ordinate system. If the motors are now coupled to a suitable drive mechanism they will cause the machine and the tracing head associated therewith to follow the line with a velocity determined by the speed setting. If during its normal operation the tracing head ceases to observe a pattern, pulses will cease to be fed to

transistors

108 and 109 and the on-pattern relay 18 will open. The opening of relay 18 will cut-off the drive because the return path for

relays

29 and 30 is through the contacts of relay 18. As the same time the on-pattern light will be extinguished because its circuit is also completed through the contacts of relay 1'8.

At any time when switch 42 is switched in the traverse direction the operator may control the operation of the machine by means of the direction switch 26. Therefore at this point if the machine has stopped because it has gone off pattern it is possible for the operator to move the switch 42 to the traverse position and push switch 26 in a direction suitable to move the tracing head once more over the pattern. When the pattern has been acquired switch 42 may be returned to the center position. At any time during the operation of switch 26 the high speed pushbutton may be pushed. This increases the voltage applied to the speed circuits and permits the machine to traverse at high speed by actuating relay 123 and opening the tachometer feedback circuit.

Other facilities are also available to the operator which have been referred to earlier. In particular, as has been indicated, the diameter of the tracing circle is related to the desired tracing speed and varying conditions will dictate varying diameters of tracing circle. To this end, the machine may be supplied with aplurality of mirror carriers 46, with different mirror angles to permit different diameters of scanning circles. 'Io substitute one for the other is only necessary for the operator to remove the sub-frame 51, remove the mirror carrier 46 and replace with the desired mirror carrier.

It is also possible that under varying conditions the degree of offset necessary to compensate for kerf will vary and this is also subject to adjustment by the operator. i

As was previously indicated the sub-frame 51 may be rotated and the degree of rotation indicated on the indicia 54 will indicate the degree of correction.

The manner in which rotation of this assembly allows for kerf may be understood if one considers that the circular scanning of thetracing head commences at zero degrees and the system attempts to maintain the crossing of the pattern coincident with the zero degree point on the circular scan. If now a radius joining the center of rotation of the tracing head and thezero degree point of the scan is parallel to the line being traced, then the center of rotation of the scan travels along the line. If on the other hand, this radius is not parallel to the line being traced, then the center of the scan is displaced from the pattern. The machine tool controlled, however, follows the center of the scan due to direct mechanical coupling and hence does not fol low the pattern but follows a point displaced from the pattern by an amount depending upon the angle of the radius with respect to the pattern. This angle is the angle indicated by the indicia 54, and hence the indicia may be calibrated in terms of actual displacement or kerf correction.

SUPPLEMENTARY DISCLOSURE The apparatus above described may be modified in various ways to fit particular situations. For example, special provision may be made to improve stability of the apparatus when the tracing head unit is remote from the amplifier. In addition, the operator may be provided with a manual steering control. These particular modifications are described in greater detail in association with FIGS. 4e and 4f.

Considering 4e, it will be seen that the phototransistor rather than being connected directly into the input of preamplifier is instead connected to an FET arranged as an amplifier incorporated in the tracing head unit. potential FET 151 is supplied with suitable potential from terminals M and L and its base is connected to the output of the photo-transistor 10. The

will be seen that the input and feedback circuit on this amplifier differs somewhat from those shown in association with amplifier 81 in FIG. 4a. It will also be noted that there is no provision for a level output. Transistors 83 and 84 are not used in this circuit but rather zenor diode 152 is applied to the input terminal of amplifier 97. This eliminates the necessity for amplifier 85 in FIG. 4a. The zenorestablishes a constant level at terminal 2 of amplifier 97 which is sufficiently accurate for the purpose.

Turning now to FIG. 4f there is shown a circuit for providing a manual steering control for the operator. This figure should be read with particular reference to FIG. 1b since the elements shown, in particular the sample and hold circuit 20 and the traverse circuit 23 occur in both circuits and the new elements of FIG. 4f are primarily introduced between these two parts of the circuit of FIG. lb.

The connectionsfrom the sample and hold circuit to mode relay 21 are the same as in FIG. 4b with the same connections to speed control 22. However, the output from the mode relay contacts rather than going solely to traverse circuit 23 are applied to an auxiliary circuit. This auxiliary circuit includes sine cosine potentiometer which is supplied with positive and negative speed signals through transistors 161'and 162 which in turn are provided with speed signals from the contacts of mode relay 21, which are applied to the bases of these transistors. The output from the sine cosine potentiometer is applied to the contacts of the steer relay 163 and may be used to replace the output from the mode relay whether it be a plus or minus speed signal or a y or x output signal. Further contacts on the steer relay will override the on pattern contacts and ensure that terminals T and W of traverse circuit 23 are grounded when steer relay is energized.

Contacts of switch 42' replace the corresponding contacts in switch 42 in control unit 37. It will be noted, for example, that the right hand contact is connected to terminal I of connector J1 on control unit 37. When switched to the traverse position, the mode relay is energized. Switch 164 enables the operator to select either steer or straight cut traverse. In its left hand position, it energizes the steer relay 163 when the mode relay is energized. When in its right hand position it grounds the contacts of the direction switch 26 in the control unit 37. As seen in FIG. 1b terminal X from switch 164 is connected to terminal X on the direction switch in control unit 137. High speed switch 165 replaces high speed switch 43 in FIG. 1b.

OPERATION Since there is no mechanically rotating element in the tracing head, it is impossible for the operator to manually steer the tracing head without this auxiliary control. To this end when the mode relay is actuated and the steer relay is actuated, plus and minus speed signals are applied to speed control 22 and the output from the speed control is applied to the contacts of mode relay and from thence to the bases of transistors I61 and 162. The resultant potential is applied across the sine cosine potentiometer 160. The operator positions the arrow on the sine cosine potentiometer control in a direction corresponding with that direction which he wishes the apparatus to move. This locates the sliders on the sine cosine potentiometer in such a manner as to provide signals on the two sliders representative of the necessary co-ordinate signals to cause the motors to drive the apparatus in a desired direction. These signals are applied to the contacts of the steer relay which is energized and therefore applies these steering signals to terminals K and V of traverse circuit 23. These signals are applied through the system to the X and Y drive motors as previously described. in this way, the operator is free to control the direction of motion of the machine-by rotation of the knob of the sine cosine potentiometer and its speed by manipulation of the speed control.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

l. A photo electric edge tracing apparatus including an optical scanning system arranged to scan a circular path on a surface bearing an optically detectable image to be traced, said optical system comprising a housing,

a subframe rotatably and removably mounted in the upper end of said housing, an electric motor mounted in said subframe, a generator arranged coaxially with said motor with two rotors fixed to the shaft of said motor and at 90 electrical degrees with respect to each other, a mirror assembly mounted on the lower end of said shaft, a lens mounted in the lower end of said housing coaxial with said motor, a photocell mounted adjacent the upper surface at the center of said lens and facing said mirror assembly, a mirror mounted on said mirror assembly'eccentric with respect to the axis of said motor with the plane of said mirror almost at right angles to said axis, said lens and said mirror arranged to focus a portion of said detectable image on said photocell whereby rotation of said mirror assembly by said motor causes the photocell to efiectively scan said surface in a circular path.

2. A photo electric edge tracing apparatus as claimed in claim 12 wherein the values of the outputs from said generator is determined at the point in time that the photocell scans the edge being traced and voltages proportional to said values are used to control motors for positioning said housing relative to said surface.

Claims

1. A photo electric edge tracing apparatus including an optical scanning system arranged to scan a circular path on a surface bearing an optically detectable image to be traced, said optical system comprising a housing, a subframe rotatably and removably mounted in the upper end of said housing, an electric motor mounted in said subframe, a generator arranged coaxially with said motor with two rotors fixed to the shaft of said motor and at 90 electrical degrees with respect to each other, a mirror assembly mounted on the lower end of said shaft, a lens mounted in the lower end of said housing coaxial with said motor, a photocell mounted adjacent the upper surface at the center of said lens and facing said mirror assembly, a mirror mounted on said mirror assembly eccentric with respect to the axis of said motor with the plane of said mirror almost at right angles to said axis, said lens and said mirror arranged to focus a portion of said detectable image on said photocell whereby rotation of said mirror assembly by said motor causes the photocell to effectively scan said surface in a circular path.