Contains reports on two research projects

Jones, J. J.

Raymond, J. A.

DSpace@MIT

X. PROCESS ANALYSIS AND SYNTHESISDr. M. V. Cerrillo J. J. Jones G. SebestyenProf. H. J. Zimmermann J. A. Raymond Rita K. ToebesA. A MACHINE THAT CONSTRUCTS PHOTOGRAPHIC REPLICAS OFCODED FIGURESAn initial report on this project was presented in Quarterly Progress Report No. 53,page 111. This report will serve to bring the reader up to date on the project and alsoexpand the points previously raised.This research is concerned with the design of a machine that will have as itsassignment the function of extracting information from a specially prepared motion-picture film of a dance routine and, with the use of this information, of assembling afigure from a stock of cutout parts. The cutout parts will be obtained from a staticphotograph of the dancer. The figure thus constructed by the machine is to be recordedby a camera. When a sequence of output recordings is assembled, a projection of thissequence can be compared with the original input information. Such a correlation willbe used to study experimentally the mathematical operator which produces estheticquality in the dance routine.A professional dancer will perform a dance routine that obeys certain constraints.These constraints are planar movements of seven parts of the body in rotation aboutsix prescribed joints. The seven parts are identified by arrows affixed to the dancer.These arrows are actually groups of four colinear spherical frosted lamps. One ofeach group of four lamps is more intense than the others. This lamp will be used togive the location of the arrow. The three less intense lamps have a twofold purpose.First, with the more intense lamp, they form an axis that defines the angular orientationof the given arrow. Second, they form a binary code that identifies each arrow with thepart to which it is affixed.The dancer with the seven arrows properly coded is supposed to perform a pleasingdance routine. The judge of the degree of the esthetic quality is a skilled dance director,John Gilland, who is in charge of designing the routine, instructing the dancer in itsperformance, and ascertaining the fact that the dance is pleasing to his esthetic senses.Thus he establishes the initial fidelity criteria.The dance routine will be recorded by means of a motion-picture camera. The filmwill be developed so that only the arrows appear. The frames of film thus prepared areto be utilized as the input information to the machine which is the basis of this project.The actual size of the arrows is determined by the spacing of photocells on a sensingdevice to be described later.The first function of the machine is the scanning of the input information. The inputis scanned in order to extract the information that it contains. A frame of input will becomposed of seven groups of points arranged in various locations, angular orientations,130(X. PROCESS ANALYSIS AND SYNTHESIS)and sequences. The frame of specially prepared motion-picture film is projected on afrosted glass surface. The scanning process must locate each of the seven intensepoints. Upon interception, the scanner orients its sensing device to coincide with thearrow direction as defined by an intense point and any of its associated points. At thesame time as the orientation is completed, the sensor determines the identity of thearrow from the binary code represented by the three colinear lights. The scanner iscomposed of three synchro devices that form the two rotations of scanning and singlerotation associated with angular alignment of the sensor with the intercepted arrow.The two rotations of scanning take the form of two arrows connected tip-to-tail similarto modulation description. The interception of the most intense point takes place at thetip of the second arrow. The third rotation occurs at the tip of the second arrow.The sensor is composed of four colinear photocells. The one that is used to detectthe interception point is coaxial with the shaft of the synchro that produces the thirdrotation. The other three photocells sense orientation and identity of the interceptedarrow.When one of the arrows has been intercepted and identified, the machine must decodethe identification information. The binary code for the given part is transformed into acommand which controls a turntable. The turntable carries the seven parts about itsperiphery. The turntable, which is rotating, will stop so that the correct part is offeredto the organizing section of the machine when the identification command is received.Each of the parts, which are cut out of a static photograph of the dancer, is prepared sothat it can be attracted by a magnetic force. The device that accomplishes the organi-zation is terminated with an electromagnet. When the selected part is placed under theelectromagnet by the turntable, the electromagnet is energized and thus picks up thepart.The device that has the task of placing the selected part in the correct position andorientation in the output field is similar to the scanner. It is synchro-connected to thescanner through a relay switching network. One state of the switching network causesthe organizer to align itself to a position identical with that of the scanner. The otherstate of the switching network causes the organizer to align its synchros so that allthree effective arrows are colinear. In this position, the end of the organizer, whichunlike the scanner is terminated in an electromagnet, is placed directly over the posi-tion where the selected parts are offered by the turntable. The figure represented bythe input frame of information points is reconstructed by the successive selection andorganization of the parts by the machine. Upon completion of the assembly procedure,a photograph is taken of the figure. The figure is then cleared from the output field,the control unit is reset and the input information updated. The procedure is repeatedagain and again until the input information is exhausted.The control of the operation of the machine is regulated by a system of switching131(X. PROCESS ANALYSIS AND SYNTHESIS)logic. The motors that drive the synchros, the synchro switching relays, theelectromagnet, the photocells, the selection turntable, and the process of projectionand recording are all governed by the transistorized control network. In addition to thepurely manipulative functions, the control logic must decide whether a given arrow hasalready been intercepted, and, finally, whether or not all seven parts have been organ-ized. The logic also incorporates a conversion matrix for the purpose of decoding theidentity of a given intercepted arrow.The machine is now being constructed. The logical blocks, utilizing approximatelyone hundred transistors, have been assembled and tested individually. Back-panelwiring is being done at this time. The intricate job of machining and assembly is wellunderway on the synchro systems for scanning and organization. Each synchro must beconnected to the outside through slip rings. The construction of slip rings on thesynchros, the interconnecting plates and bearings, of the selection turntable, and of atable to contain the entire machine should soon be completed. The synchromotor trans-mitter assembly has been constructed.The services of a professional dancer have been acquired. The training of thisdancer is now going on.A more detailed operational account can be found in the author's S.B. thesis entitled,"A Machine That Constructs Photographic Replicas of Coded Figures," submitted to theDepartment of Electrical Engineering, M. I.T., May 25, 1959.J. A. RaymondB. ELECTRONIC CURVE TRACINGElectronic curve tracing finds an application in the fields of pattern recognitionand identification techniques. A curve-tracing machine such as is described here isused for the purpose of automatically tracing the contour of a simple black and whitesilhouette. More precisely, a silhouette is defined as an arbitrarily positioned, two-dimensional closed curve, the interior of which is blackened and contains no holes.The desired result of tracing the contour of a curve is the X and Y coordinates as aparametric function of peripheral distance. To obtain these coordinates as a functionof time, the curve may be traced with a constant peripheral velocity. Other suitableparameters for uniquely describing the curve can be derived, if required. Fourier-series analysis of the curve is possible if the tracing is carried out in a periodicmanner.In particular, the tracing machine employs a flying-spot scanner with associatedoptical system and phototube. The silhouette is presented in the form of a transparencyon which the light output of the scanner is focused. The light that passes through thetransparency is collected on the cathode of a phototube and converted to video infor-mation. The heart of the machine is a dual-channel analog servo system which provides132(X. PROCESS ANALYSIS AND SYNTHESIS)all of the automatic controls and supplies the X and Y coordinates. A pictorial diagramof the complete system is shown in Fig. X-1.Since the silhouette is arbitrarily positioned, it must first be located before itscontour can be traced. Therefore, two distinct modes of operation are required of themachine, one of searching for the curve and the other, of tracing the curve. Thesearching mode is instrumented with the use of a spiral sweep that seeks out thesilhouette, as shown in Fig. X-2. At the first intersection of the sweep with theboundary of the silhouette, the intensity of the light passing through the transparencydrops to a minimum and thus causes an abrupt change in the video signal. A differen-tiator operating on the output of the phototube then provides a trigger pulse to instructthe machine to hold the coordinates of the point of intersection and to switch to thetracing mode.The problem of tracing the periphery of the curve can be broken down into twoseparate operations:(a) The scanning spot must be kept centered on the contour of the silhouette.(b) The spot must be caused to move along the curve.Both of these operations can be facilitated by causing the scanning spot to rotate in acircular path and thus describe a circle. The circle size is assumed to be small com-pared with any important detail in the curve and the speed of rotation of the spot islarge as compared with its speed of translation along the curve. Thus the silhouette ispictured as being traced out by a very small circle that moves slowly along its contour.A circle is, of course, easily generated by the addition of sine and cosine waves to theX and Y coordinates. As the scanning spot moving on a circle crosses the boundaryof the silhouette into or out of its blackened interior, the video output changes abruptlyfrom a high to a low value, or vice versa. Hence, the derivative of the video waveformprovides a timing reference.Ideally, the circle should be centered on the curve but without a restoring force itwould tend to drift away to an uncentered position. As shown in Fig. X-3a, the circleintersects the silhouette as a chord rather than as a diameter. To center the circleon the curve requires that a point halfway between the ends of the chord coincide withthe center of the circle. The differences of the X and Y coordinates of these twopoints are error voltages that could be applied to a zero-position-error servo system tomake the points coincide. However, if we think of the circle as a perturbation aboutits center that is considered as an average value, then the center of the circle can beused as a new origin of coordinates for errors. Therefore, it is sufficient to deal onlywith the sine and cosine parts of the X and Y voltages. The error coordinates x l , y 1and x Z, Y 2 of the ends of the chord are obtained by sampling the sine and cosine waveseach time the scanning spot crosses the boundary of the curve. The mean-errorcoordinates of the chord are then133FLYING - SPOT FOCUSING CONDENSINGSCANNER LENS LENSPHOTO TUBETRANSPARENCYCONTROLLER ANDCOORDINATE EXTRACTORCONTROL SIGNALS VIDEOAND COORDINATES X CHANNEL INFORMATIONY CHANNELFig. X-1. Curve-tracing machine.SPIRAL SWEEPFig. X-2. Searching for the curve.134(X. PROCESS ANALYSIS AND SYNTHESIS)xo= / (x + x)Y = 1/2 (yl + Y2)and the coordinates of the center are 0, 0. Hence, x0 and yo are the total x and y errors,and if they are integrated and added to the coordinates of the center of the circle theywill cause the circle to be centered on the curve.x = 1/2(X +x 2 )XYO = 1/2 ( + y2) x -X20 0,0(a) (b)Fig. X-3. Tracing the curve.If we consider that the circle is already centered on the curve, a diameter of thecircle is now tangent to the curve with the point of tangency at the center of the circle,as shown in Fig. X-3b. For a fixed circle diameter, the tangent is a line segment offixed length, but changing direction, as the circle moves along the contour. Hence, thetangent has all of the characteristics of a velocity vector of a point moving along a curvewith constant speed. The x and y components (xl - x 2 and yl - yZ) of this vector alwaysadd vectorially to a constant length, and if they are integrated and added to the X andY voltages they will cause a net translation of the circle in the direction of the tangentvector. Thus the center of the circle moves along the contour of the curve with aconstant tangential speed. The total X and Y voltages before the addition of the sineand cosine waves are the coordinates of the center of the circle and of the curve.Hence, the machine has achieved its desired result.Throughout this discussion it has been tacitly assumed that the circle size, forobvious reasons, is small compared with any important detail of the curve. Further-more, it has been assumed that the speed of rotation of the spot is large compared withthe speed of translation; that is, the circle frequency is much larger than the frequencyof tracing around the contour. Because x 1 , Yl and x 2 , y2 occur approximately one-half the period of the circle frequency apart, they cannot be measured simultaneouslyand therefore a large error could result. However, if the circle frequency is of theorder of 1000 times the frequency of tracing, little error should result, in practice.135I h(X. PROCESS ANALYSIS AND SYNTHESIS)TI T I +8NO. I KISAMPLE AND 2 INTEGRATOR S (+x2)HOLD NO. I NO. r TI+8sin w0tX SWEEPTOELECTRONIC + SCANNER+ XX4. The Xch e otea isin wot + X COORDINATE SWITCHT 2  T I +8 TISAMPLE AND x x 2 INTEGRATOR SAMPLE ANDHOLD NO.2 NO.2 2 HOLD NO. 3NO.2 S(x X 2)w = CIRCLE FREOUENCYFig. X-4. The X-channel of the tracing machine.Fig. X-4 shows a block diagram of the X-channel of the machine. The Y-channelis identical except for the replacement of the sine with a cosine and the X-sweep withthe Y-sweep. The following description also applies to the Y-channel. The machinestarts its operation in the search mode with the X-sweep feeding through the electronicswitch to the flying-spot scanner. Operation continues in this state until the sweepintersects the silhouette, at which time (T 1 ) a trigger pulse occurs. This pulse causesthe sample-and-hold circuit No. 3 to hold the value of the X-sweep at the time of inter-section, which is the initial X coordinate of the curve. As soon as this operation iscompleted, the electronic switch is triggered (at time T 1 + 6). The initial X coordi-nate now feeds through the switch from the sample-and-hold circuit. The machine isnow in the tracing mode and the electronic switch remains in its present state. At theinstant of intersection, sample-and-hold circuit No. 1 measures the initial value (x 1)of the sine wave and the integrators start supplying a correction to the X coordinate.The next time (T 2 ) the scanning spot crosses the curve, sample-and-hold circuitNo. 2 measures a new value (x 2 ) of the sine wave and completes the measurement oferrors.The output of the summing circuit No. 1 is now proportional to the mean coordinateof the intersected chord (x° = 1/z x1 + 1/2 x 2 ) and the output of the summing circuit No. 2is the length of the x component of this chord. Integrator No. 1 supplies an X correc-tion to center the circle on the curve and integrator No. 2 supplies the X component ofthe displacement that is necessary to move the circle along the curve with constantspeed. These integrators have individual gain controls for adjusting independently theloop gain of the centering servo and the speed of tracing of the curve. The outputs ofthe integrators are added to the initial X coordinate of the curve to produce a new136(X. PROCESS ANALYSIS AND SYNTHESIS)corrected X coordinate. When the scanning spot crosses the curve again, sample-and-hold circuit No. 3 measures the new value of the X coordinate. As soon as thisoperation is completed, the integrators are reset to zero and the cycle of operations isrepeated. Resetting the integrators is necessary, since each new output of the sample-and-hold circuit No. 3 contains the past corrections made by the integrators. Thedischarge of the integrators exactly cancels the discontinuities in the output of thesample-and-hold circuit. Thus the machine traces out the curve.J. J. Jones137

Process Analysis and Synthesis

http://dspace.mit.edu/bitstream/1721.1/52288/1/RLE_QPR_054_X.pdf

Process Analysis and Synthesis

Abstract

Similar works

Full text

Available Versions

DSpace@MIT