Abstract: A servo device for use with a system for reading out recorded information having at least two pickup elements which produce pickup signals comprising a resistance network including at least a resistance through which at least two of the pickup signals flow, and an error signal producing device for producing a tracking error signal and a focusing error signal in accordance with a voltage level developed at a terminal of the resistance, whereby eliminating the use of a plurality of amplifying circuits and adder circuits which are respectively connected to each of pickup elements, and enabling the production of more accurate error signals and reduction of the cost of the servo device.

Abstract: A device makes it possible to eliminate the imbalance of a deviating mirror of an optical system which illuminates a data medium or support when that mirror is subject to rapid displacement. The imbalance is cancelled by the use of a photodetector device which receives the light reflected by a reflecting element positioned around the objective of the optical system which illuminates the medium. A control device then makes it possible to control the position of the mirror based upon the light given off by the reflecting element.

Abstract: Apparatus for adjusting the position of an edge between two surface porti of a moving belt with different spectral reflectivities where required in connection with work or treatment needed along the edge of one of the two surface portions while the belt is moving. It is a pre-requisite condition that the mutually adjacent surfaces of the belt are sufficiently significantly optically detectable which is impaired, for example, in the presence of surface contamination by dirt and the like. In order to obtain a significant signal in such circumstances, the edge region is illuminated and an imaging or focussing lens associated with a beam splitter is arranged in the focus beam. Following the beam splitter the two part-beams pass through one filter each to impinge on in each case a photodiode receiver, each filter blocking passage in that wavelength range in which the other filter is transmissive.

Abstract: A pattern tracer and method of tracing in which the movement of a racing element along a pattern is controlled in accordance with an effective forward offset which is selectively less than the actual forward offset to optimize the tracing for speeds less than the maximum tracer speed. The effective forward offset is established by providing control angles which are based on the pattern angles as detected in accordance with a selected criterion depending upon the type of pattern curve detected. The control angles are either calculated from the detected pattern angles or are selected from previously stored pattern angles. A kerf setting for lateral offset of the tracing element from the pattern is partially defined by the actual forward offset, so that changes in the effective forward offset do not cause any corresponding changes to the lateral offset or require changes to the kerf setting.

Abstract: An automatic running work vehicle in which both front wheels and rear wheels can be steered and which is provided with a follower sensor for detecting the boundary between an unworked area and a worked area and an orientation sensor for detecting the running direction so as to run automatically along the boundary. Based on the result of detection of the boundary by the follower sensor and on the result of detection of the orientation of the vehicle body by the orientation sensor, the front and rear wheels are steered automatically to correct the running direction automatically.

Abstract: An optical output device comprising a deflector having an electrooptic crystal element provided with an electrode and controlling an electric field applied to the electrode to vary the deflection angle of a light beam passing through the crystal and projecting the beam upon a predetermined position on a recording medium and separating the reflected light from the recording medium from the light beam or/and a variable focal length lens consisting of an electrooptic crystal and which uses a condenser for controlling the focal length of the lens by an electric field applied to the crystal and focusing the light beam to the recording medium, thereby reducing the number of mechanically movable parts of the device.

Abstract: A robotic vehicle is guided along a predetermined path which is to be traversed autonomously by the vehicle. As the vehicle is guided along the path, the area before the vehicle is scanned and discontinuities in the scan scene are reduced to a series of time separated pulses. The pulse series at selected locations along the path are stored such that the vehicle can autonomously retrace the predetermined path by matching pulse series generated by current scanning with stored pulse series. A scanner mirror receives and directs a laser beam through an area before the vehicle along the path to be traversed and receives reflected return signals from the scanned area. Optical detection means receive the return signals from the scanner mirror and generate raw scene signals which are doubly differentiated to generate pulse series representative of the discontinuities of the scanned area.

Abstract: A measurement head in an arc welding machine modulates the light intensity of a laser light beam with a modulating signal of 50 KHz or higher, and radiates the laser light beam onto an object to be measured while changing the direction of laser beam emission in one plane. A light receiving unit in the measurement head changes its direction of detecting a reflected beam in the same plane. Angles at which the light beams are emitted and detected are detected at the time a modulated signal component is detected from an output from the light receiving unit. The position of a bright spot produced on the surface by the radiated laser light beam is computed from the detected angles based on the principle of triangulation.

Abstract: A tracking servo system of a recording-disc reading and reproducing apparatus in which the information carried on a recording disc adapted to be driven for rotation is scanned by a signal pickup point displaced radially of the disc, comprising tracking error signal generator operative to detect an amount of deviation, if any, of the signal pickup medium from a target track on an information-carrying surface of the recording disc and produce a tracking error signal representative of the detected amount of deviation, and band eliminator such as a notch filter operative to eliminate a predetermined frequency in the tracking error signal.

Abstract: An apparatus for tracing and recording image lines includes a coordinate reader which detects coordinate values of an image to be traced; an image sensor which is movable in a plane relative to a table; a memory in which image signals detected by means of the sensor are written; and a central processing unit which controls the above elements of the apparatus. Trace data are obtained by means of the coordinate reader which detects coordinate values of the image lines. Then, the image is positioned on the table, where record data are obtained based on the trace data by means of the image sensor which generates image signals corresponding exactly to the image.

Abstract: A tracking error of a light spot focused on an optical record disc by means of an objective lens with respect to an information track recorded on the disc is detected by processing outputs from a light detector arranged in a far field of the track and having four light receiving regions on which a light reflected by the disc is incident. A tracking error signal of a differential detection system, i.e. a difference between two sums of outputs from two pairs of two regions aligned in a direction tangential to the track is derived, and a push-pull signal, i.e. a difference between two sums of outputs of two pairs of two light receiving regions aligned in a radial direction is also obtained.

Abstract: A device for optically tracking information recorded on an optical disc wherein a photodetector is disposed on the optical axis of an optical system for guiding diffracted waves to the photodetector. The origin of a fictitious X-Y coordinate system at the photodetector is placed on the above-mentioned optical axis, X- and Y-axes of the coordinate system are made parallel to and perpendicular to an information track having the information pits on the rotating recording medium, and the photodetector is divided into four equal parts. A first summation signal indicating the sum of output signals from the four parts of the photodetector is converted into a binary signal, and a difference signal between second summation signals each indicating the sum of output signals from a pair of photodetector parts facing each other with the origin of the coordinate system therebetween is converted into another binary signal.

Abstract: An optical recording apparatus wherein in front and rear of a first light spot for recording predetermined information along a guide groove provided in a recording medium beforehand, two second light spots and two third light spots are arranged along the guide groove and in a manner to mutually deviate from the center of the guide groove; the second light spots are arranged in an area with no information recorded therein, while the third light spots are arranged in an area with the information recorded therein; and the position of the first light spot is controlled on the basis of the difference between the quantities of light of the second light spots and the difference between the quantities of light of the third light spots, so as to track the information.

Abstract: A tracking system for optically tracking information tracks formed on a recording medium, comprising a comparator which generates a trigger signal when the light beam scanning the information track is located over an information pit, and a sample holding circuit which samples a deviation signal caused by the difference of reflection light intensities on two photo detectors at that time. The deviation signal obtained when the light beam is located over the information pit includes smaller error component caused by the displacement of the object lens during the tracking control, whereby the accurate tracking control can be achieved.

Abstract: An optical thin line-tracking sensor comprises a small member mounting ends of a light source fiber and a pair of receiving fibers which receive reflected light. Reflected light transmitted through the receiving fibers operate photosensors whose outputs are differentially combined to provide a tracking error signal. Augmenting circuits enable operation over a wide range. Means to sense other indicia carried on a web or sheet are disclosed. A line-tracking head which includes a laser-light cutter is also disclosed.

Abstract: This invention relates to a body height and weight measuring machine, which operates by means of a winding transmission cord means to drive a sliding plate having sensing, measuring, and digital display functions. When the sliding plate moving upwards, the sensing means will receive the refracted infrared rays as a result of a person's height to cause said winding transmission cord means to stop moving; then, a correct height and weight will be displayed thru digital display means. The aforesaid height measurement and its digital display are done by means of a photocell sensing means being coupled to a scale plate that includes a black and transparent strip in alternate arrangement and equal width so as to have said photocell sensing means generating a forward or reverse sequence sensing signal during the sliding plate moving; then, said signals will be shown on a display means driven with driving circuit.

Abstract: A tracking servo system of a video or audio disc player, wherein the control data signals extracted from the electric signals read out from an information-carrying face of a video or audio recording disc are inhibited from being delivered from the servo system when the servo loop forming part of the system is open.

Abstract: A tracking servo signal generating device in a tracking servo control system in a recorded information reading apparatus adapted to deviate an information detecting point in the direction perpendicular to a target recording track on a recording medium in accordance with the tracking servo signal so that the information detecting point accurately traces the recording track, which comprises detecting means for producing a pair of detection signals a difference between which represents amount and/or direction of deviations of the information detecting point from the recording track in the direction perpendicular to the track. The pair of detection signals is processed to produce a first difference between low frequency components of the detection signals and a second difference between envelope components of high frequency components of the detection signals.

Abstract: The performance of prior automated welding systems has been limited by their inability to independently track and weld and by their inability to accurately determine the groove profile. The adaptive welding system disclosed herein includes a weld torch (20) adapted to be controllably positioned in at least two dimensions, and means (28,38) for tracking a workpiece seam (12) to be welded. The tracking means (28,38) is pivotably connected to the weld torch (20). Means (19,40) for pivoting the tracking means (28,38) relative to the weld torch (20) is included to permit both the tracking means (28,38) and the weld torch (20) to be independently maintained over the seam (12). The tracking means (28,38) monitors the seam (12) by optical triangulation of a rotating laser beam (60) projected against the workpieces. This rotating laser beam (60) crosses the seam twice during each cycle of the beam (60).

Abstract: In an optical video disc player, a still picture mode reproduction is effected by returning a light spot on an optical video disc by one track pitch in its radial direction after each revolution of the disc. The displacement of the light spot is carried out by supplying a returning pulse to a moving coil coupled with an objective lens to move the objective lens in a disc radial direction. In order to cause the light spot to trace a track precisely, a tracking error due to an eccentricity of the disc is detected and the objective lens is moved in the disc radial direction in accordance with the detected tracking error. An amplitude of the returning pulse is modulated in accordance with a velocity component of the displacement of the objective lens under the tracking condition, so that the light spot is returned accurately by one track pitch.

Abstract: A scanning angle tracker which includes a laser beam and a beamsplitter for developing two beams which intersect on a scanning mirror. The scanning mirror sweeps the two beams across a retro-reflective tape on the object. Return signals are generated for processing to provide the desired angular information.

Abstract: A device for controlling the glue nozzles of a machine for gluing together at least two paper webs provided with recurring form designs to produce multi-part sets of continuous forms. The control device has at least one sensing element and at least one glue nozzle which are both connected to a computer. Also connected to the computer is a displacement transducer for determining the position of the beginning of a form with respect to the respective glue nozzle. In a "read-in" mode, the sensing elements senses a specially treated read-in form, and the values obtained are stored in the computer. In a second mode, the "glue" mode, the computer activates the glue nozzles precisely when the displacement transducer provides an address for which a "glue" instruction was stored during read-in.

Abstract: A video disc player is described for use with a video disc having frequency modulated video information recorded thereon in the form of a plurality of concentric circles or a single spiral. The information track comprises successively positioned light reflective and light non-reflective regions. A focused light beam is caused to be positioned over the center of an information track and the light reflected from the information track is gathered by an objective lens for application to electronic circuitry for recovering the recorded frequency modulated video signals. Radial tracking means are described for maintaining the focused light spot to impinge upon the center of an information track. Lens focusing means are described for positioning the objective lens at the optimum focused position above the information track for gathering the maximum amount of reflected light from the information track.

Abstract: An optical pattern tracing system of the type having a tracing head with a scanner that projects a photocell onto a pattern-line with an improved manual resolver for providing control signals to drive the tracing head in an approach direction toward the pattern-line. The manual resolver is a capacitive resolver constructed of foil elements and an angularly adjustable coupling disc mounted directly on a printed circuit board that also carries much of the other control circuitry for the tracing system.

Abstract: An optical information reproducing apparatus comprises an optical system adapted for shifting a light spot to impinge upon a track of a disk and for condensing the reflected light beam so as to impinge upon a photodetector. The output of the photodetector is sampled at predetermined intervals so that the envelope value thereof may be read. Successive envelope values, as sampled, are compared to provide a difference signal thereof. An error signal is obtained based on the positive or negative difference signal. The position of the light spot is adjusted as a function of the error signal.

Abstract: Disclosed is an electro-optical and microcomputer based method and apparatus for automatically guiding tractors and other farm machinery for the purpose of automatic crop planting, tending and harvesting. Also disclosed are means for automatic picking, excavating and other off-road uses in relatively confined areas.

Abstract: An apparatus for driving an objective lens which projects a light spot onto an information track or tracks recorded spirally or concentrically on a disc-shaped record medium to read out information, in order to correct a tracking error, comprises a pair of leaf springs for supporting the objective lens movably in a tracking direction perpendicular to the optical axis of objective lens as well as to the track direction, a movable member made of magnetic material and being coupled with the movable member to move in the tracking direction in conjunction with the objective lens, first and second magnetic members made of magnetic material and arranged in such a manner that the movable member is interposed between the first and second magnetic members at their one end portions via gaps, a third magnetic member made of magnetic material for coupling the first and second magnetic members at their other end portions, first and second coils wound on the one end portions of the first and second magnetic members, respect

Abstract: A tracking control apparatus for use with an optical information reproducing system in which information to be reproduced is formed on a surface of a recording carrier with a substantially circular record track, and a light beam is incident on the surface for reading the information, the apparatus including a photo-detector for detecting the light beam reflected from the recording carrier and generating an information signal and a first tracking error signal, the first tracking error signal being responsive to deviations by the light beam from the center of the record track; a tracking control apparatus receiving the first tracking error signal for adjusting the position of the light beam in response thereto; a measuring device for generating a second tracking error signal indicative of the eccentricity of the record track; and a circuit for supplying the second tracking error signal to the tracking control apparatus to adjust the position of the light beam in response thereto.

Abstract: An optical pattern tracing system of the type having a tracing head with a scanner that projects a photocell onto a pattern in a closed path and provides two signals for each complete path across a line with an approach control for driving the tracing head toward the pattern-line that permits the operator to preselect either clockwise or counterclockwise tracing. The tracing head approach control includes circuitry that selectively blocks the first or the second pulse from the photocell and then terminates the blocking function shortly after the line is reached. An improved line detector is also disclosed that detects the true center of the line to be traced, and a dual pulse detector is also provided that assures that the scanner is fully locked onto the line prior to switching from manual to automatic control.

Abstract: An optical read system for a disk-shaped record carrier. By means of a tracking system the read spot is centerd at the information track. The control signal for this tracking system is obtained by means of additional radiation spots which are disposed on radially opposite sides of the read spot. By subjecting the detection signals corresponding to these additional radiation spots and the read spot to a special operation a control signal is obtained which is highly independent of variations in disk parameters, variations in the intensity of the radiation beams and focussing errors.

Abstract: A scanning angle tracker which includes a laser beam and a beamsplitter for developing two beams which intersect on a scanning mirror. The scanning mirror sweeps the two beams across a retro-reflective tape on the object. Return signals are generated for processing to provide the desired angular information.

Abstract: A method for tracing an object such as an outline of a picture or a line image, wherein the object is sensed by a set of sensing elements arranged in an optical head moving along the object, to detect a position and a direction of the object, wherein the optical head is controlled to trace the object depending on the detected position and the direction of the object, and wherein the object is reproduced by reproduction means which is moved in synchronization with the optical head. Present invention improves this method by moving the optical head along portions of the object, which the sensing elements can discriminate hardly or not at all nor follow the object, according to line segment data which is predetermined and represent a plurality of points of coordinates.

Abstract: In a method and a circuit for determining a contour-defining angle formed by a contour in an image within a relatively small region thereof with a predetermined direction, the steps include selecting the region so that said contour passes as closely as possible through a center thereof, and subdividing the region into a number of sectors of substantially equal areas distributed substantially symmetrically about its center, and separated from one another by respective separation lines, the number being an even number and at least four, and one of the separation lines coinciding with the predetermined direction, obtaining brightness signals from each of the sectors in dependence of the proportion of the dark-to-light areas extending over each respective sector, generating difference signals from respective oppositely disposed sectors, processing the difference signals so as to identify the sector in which the transition from the light area to the dark area occurs, and determining by further processing the conto

Abstract: A laser beam, while moving in a radial direction of a rotating optical disc, illuminates the surface of the rotating optical disc and a portion of the laser beam reflected on the surface of the optical disc is directed to a fixed photosensor. The photosensor includes a plurality of photoelectric elements arranged along the radial direction of the disc. The fixed photoelectric elements thus receive the portion of the reflected laser beam as the beam moves in the radial direction of the optical disc, and produce corresponding photoelectric signals. The photoelectric signals are read out in a time series and converted to sampling pulse signals. A sawtooth signal is generated and sampled by the sampling pulse signals. A difference detector detects the difference between a sampled signal component of the sawtooth signal and a reference voltage to determine the beam position based on the detected difference.

Abstract: An apparatus for reading and/or writing an optically readable information structure, arranged in information tracks, on a record carrier, comprises a beam deflection element which is controlled by a control signal obtained from a tracking servo system. The apparatus is provided with a position detection system for detecting the position of the deflection element, and the signal from this detection system is applied to an input of the servo system for generating a control signal which is independent of the position of the deflecting element.

Abstract: In order to track a distinctive line on a workpiece area to be followed by an operating implement, specifically a junction line between two workpieces to be welded by a torch advancing along that line, a narrow beam is trained generally perpendicularly from a pulsating source of luminous radiation--e. g. a laser--upon that area and is shifted parallel to itself around the implement so as to intersect the workpiece area along a closed trace substantially bisected by the line being tracked. The source of radiation is part of a photosensor including an objective with an optical axis inclined to the beam at a small angle to generate an image of the latter on a slanting straight line parallel to a central ray which passes through the point of intersection of the beam axis with the front focal plane of the objective, this image line starting at the intersection of the rear focal plane with a central ray parallel to the beam.

Abstract: Data recorded in non-parallel arcuate paths on a data carrier are read with a laser beam which rotates relative to the data record.

Abstract: An optical system for recording information on or retrieving information from a rotating disc is disclosed herein. In this system a beam of light located on one side of the disc is directed onto and laterally across a given track of the disc. The track serves to contain the recorded information and, ignoring this information, is characterized by a predetermined light transmissivity curve in its cross-direction. An arrangement for maintaining the beam and given track in a fixed lateral position relative to one another as the disc rotates, even if the track moves laterally to a limited extent from its intended path of movement, is also disclosed herein.

Abstract: A control system for use in controllably adjusting a prescribed characteristic of a beam scanning a record medium. In the preferred embodiments, the control system is embodied in a tracking apparatus for use in a playback system for recovering information from a selected recording track on an optical record medium such as a video disc. The tracking apparatus produces a tracking error signal representative of the deviation of a scanning reading beam from the centerline of the selected track, and couples this error signal to a movable tracking mirror to form a servo for controllably positioning the beam in alignment with the track. The tracking apparatus further includes a dimple compensation circuit for monitoring the tracking error signal and producing a tracking loop disable signal whenever it determines that the reading beam is scanning a video disc defect, such as a dimple.

Abstract: The invention relates to a system for detecting and locating surface discontinuity by a light beam; it is more particularly intended for detecting any discontinuity forming a line on this surface, or any discontinuity forming two opposite lines on this surface. In the latter case, this discontinuity may, for example, be the join defined by the opposite edges of two metal sheets to be welded.

Abstract: Tracking apparatus and related method for use in a playback system for recovering information from a selected recording track on an optical record medium such as a video disc. The tracking apparatus produces a tracking error signal representative of the deviation of a scanning reading beam from the centerline of the selected track, and couples this error signal to a movable tracking mirror to form a servo for controllably positioning the beam in alignment with the track. The tracking apparatus further includes a defect detection circuit for monitoring the tracking error signal and producing a pair of control signals that indicate when video disc defects of prescribed types are being scanned, and a threshold detector circuit for comparing the error signal to prescribed positive and negative thresholds that are selectively-variable in accordance with the pair of control signals.

Abstract: A servo-positioning system for controlling the positioning of a read-out light beam in an optical system which reads out digital information from a pre-recorded disc including a wobbling means for wobbling a read-out beam to traverse an information track of the disc, a photo detecting means for detecting the read-out beam reflected from the disc, a waveform arranging means for arranging the output of photo detecting means, an extracting means for extracting a clock signal component from the output of the waveform arranging means, a latch circuit for latching the output of the waveform arranging means synchronized with the output signal of the extracting means, a subtracting means for subtracting the output of the latch circuit from the output of the photo detecting means, to isolate the wobbling signal component from the output of the composite photo detecting means including an information component and a wobbling component.

Abstract: An optical pattern tracer is disclosed, of the circular scanning type. The interception of the pattern by the scan produces electrical outputs which are reduced to numerical values representative of their time of occurrence with reference to the scanning circle. The numbers derived and the nature of the signal generated are then processed to indicate the direction of the pattern, presence or absence of command marks and combined with other reference inputs, such as kerf and direction of tracing used to control a drive mechanism to move the tracer around the pattern.

Abstract: A speed controlled conveyor system in which the motor driving an input conveyor is speed regulated to control the axial product pressure. This pressure is measured by the outward bowing of the column of articles as it moves along a downwardly curving chute connecting the conveyor and the loading device. A photocell arrangement measures the degree of displacement of the column and transmits a corrective electrical signal to a motor speed control device.

Abstract: A method for recording and reproducing information characterized in that an information train in which synchronizing signals are arrayed at equal time intervals between information signals is recorded in an information track on a recording medium which is wobbled in synchronism with the synchronizing signals and at a frequency integral times the frequency of the synchronizing signals, that the information train recorded in the information track is read out by read-out means, and that a position of the read-out means is controlled on the basis of the information train read out. The wobbling waveform is 90.degree. out of phase with a harmonic component of the synchronizing signals.

Abstract: A window generation circuit is provided for gating image signals from an electronically scanned sensor array in a line tracing machine. The window generation circuit includes two shift registers of variable length for measuring intervals of time for setting first and second bounds to a sector scan. The interval of the second register corresponds to the width of the window. Logic circuitry, responsive to the detection of image data, alters the electrical lengths of the registers to enlarge the window in the absence of an image, and restores the original lengths upon return of the image.

Abstract: An optical scanner for a pattern tracing system for scanning an irregular two-dimensional pattern using an optical beam deflection principle. A scanning head is non-rotatably mounted above the pattern on a frame moveable in two coordinate directions. The scanning head reflects an image onto the pattern by a pivotally mounted mirror in the scanning head and is deflected at high frequency in two normally orthogonal planes by the interaction of a pair of perpendicularly related electromagnets with a permanent magnet. The geometric axis of the mirror nutates around a scan axis to provide a generally circular scan image on the pattern. The axis about which the mirror nutates, referred to as the scan axis, is shiftable from a fixed reference axis to achieve offsets for the scan image to provide both forward offset and "kerf" offset perpendicular to the forward offset. A control circuit derives out of phase alternating signals for the two scanner coils to cause this nutational motion of the mirror.

Abstract: An optical read unit is described for scanning a record carrier with a radiation-reflecting trackwise-arranged information structure. The read unit utilizes a diode laser which generates the read beam and also detects the information stored on the record carrier. The read unit is also provided with an opto-electronic system for detecting the position of the read spot relative to a track to be read and the position of the plane of focussing. The diode is mounted in a housing and the unit includes electromechanical apparatus for moving the housing in two perpendicular directions so as to correct the position of the read spot. The objective system for the formation of the read spot is of simple construction.

Abstract: Eccentricity control apparatus is provided in a system for optically recording and reading information on a rotating disc medium. The information may be recorded on concentric or spiral tracks. The eccentricity control apparatus includes a detector for detecting track crossings as an optical scanning head scans the disc surface. The detector provides pulses representative of track crossings. The number of pulses in a once-around is representative of the amplitude of an eccentricity control signal. The angle measured between a once-around pulse and a minimum pulse rate of the track crossings indicates the phase of the error. An eccentricity error signal which is generated by suitable circuitry is applied to affect the manner in which the optical scanning head scans the disc surface such that number of track crossings is reduced.

Abstract: A video disc player is described for use with a video disc having frequency modulated video information recorded thereon in the form of a plurality of concentric circles or a single spiral. The information track comprises successively positioned light reflective and light non-reflective regions. A focused light beam is caused to be positioned over the center of an information track and the light reflected from the information track is gathered by an objective lens for application to electronic circuitry for recovering the recorded frequency modulated video signals. Radial tracking means are described for maintaining the focused light spot to impinge upon the center of an information track. Lens focusing means are described for positioning the objective lens at the optimum focused position above the information track for gathering the maximum amount of reflected light from the information track.