Abstract: An information recording apparatus includes a rotating section for rotating an optical disk at a constant angular velocity, the disk including a spiral recording track or concentric recording tracks, a recording section for recording information with a light beam irradiated on the recording tracks of said optical disk, the light beam having an arbitrary recording frequency, and control means for controlling the recording section such that the information is recorded on the optical disk while a pitch between adjacent record pits is elongated as a position of a recording track is moved from an innermost track toward an outermost track, the pitch at the innermost track being a first pitch, the pitch at the outermost track being a second pitch, the pitch at a track between the innermost and outermost tracks being longer than the first pitch and shorter than the second pitch, and the second pitch being shorter than a third pitch expected at the outermost track when the optical disk is rotated at the constant angul

Abstract: In the present invention, there is provided an optical disk medium wherein a ROM region having data already recorded therein and capable of only optically reproducing (reading) the data as well as a RAM region capable of optically recording and reading out therein and therefrom are interlacedly located in such a positional relationship that enables the substantially continuous and high-speed accessing operation to the read-only ROM and rewritable RAM data, and some of stationary data to be stored suitably in the ROM region are stored in positional relationship closer to some of additional data to be stored suitably in the RAM region which are especially closely related to the some of the stationary data.

Abstract: An optical information storage medium is used for recording optical information therein and reproducing optical information therefrom. The optical information storage medium includes parallel, concentric, or helical tracking guide grooves and information tracks defined between the tracking guide grooves. A preformat area composed of discrete pits is disposed on some of the information tracks. The tracking guide grooves and the preformat pits are defined in one surface of a transparent substrate, and a recording film capable of absorbing and reflecting light is disposed on said one surface of the transparent substrate. The ratio of the effective depth of the tracking guide grooves to the wavelength of a recording/reproducing laser beam within the transparent substrate is in a certain range, and the ratio of the effective depth of the preformat pits to the wavelength of the recording/reproducing laser beam within the transparent substrate is also in a certain range.

Abstract: An apparatus for recording and reproducing information using an optical card comprising a memory region in which one pit train for supplying a track servo signal and a synchronizing signal is formed at a edge portion of the memory region. The optical card achieves increased storing capacity by including only one pit train. The recording/reproduction apparatus for the card has a first and second optical heads. The first optical head scans the pit train to obtain the track servo signal and a synchronizing signal. The second optical head is used for recording and reproducing information from the optical card.

Abstract: The present invention concerns an arrangement for reading an optically readable light reflective carrier on which data is stored in the form of diffractive elements which are deviations from a reference surface. The data elements each have a plurality of adjacent tracks located on the carrier with data elements being positioned on adjacent tracks. The system utilizes an illumination device for projecting a concentrated light spot onto the carrier in order to obtain diffraction of light along the entire length of each of the data elements with an optical arrangement collecting light reflected from a carrier in such a way that light energy which is received when a projected light spot impinges on the reference surface is greater than the light energy received when the projected light spot impinges on a data element.

Abstract: The present invention concerns an arrangement for reading an optically readable light reflective carrier on which data is stored in the form of diffractive elements which are deviations from a reference surface. The data elements each have a plurality of adjacent tracks located on the carrier with data elements being positioned on adjacent tracks. The system utilizes an illumination means for projecting a concentrated light spot onto the carrier in order to obtain diffraction of light along the entire length of each of the data elements with an optical arrangement collecting light reflected from a carrier in such a way that the light energy which is received when a projected light spot impinges on the reference surface is greater than the light energy received when the projected light spot impinges on a data element.

Abstract: An amplitude difference between a reproduction signal from a preformat portion of an optical disk and a reproduction signal from a recording portion of user's data is obtained. When the amplitude difference exceeds a predetermined value, a first gain value which was set for information from the preformat portion is used as a gain value of an AGC circuit for reproduction and a gain control of the reproduction signal is performed. On the other hand, when the amplitude difference is smaller than the predetermined value, a second gain value which was set for the user's data is used. Thus, a situation such that a noise and a remaining signal of the user's data which was not erased are erroneously recognized as an inherent reproduction signal can be prevented. A discrimination to see if the data has been recorded in the recording portion of the user's data or not can be also accurately performed.

Abstract: An information reproducing apparatus detects a reproducing area on a disk having information recorded thereon at an approximately constant linear velocity. A reproduced signal is generated by rotating the disk mounted on a shaft of a motor, and reading out the information recorded on the rotating disk with an information reproducing head. A frequency detecting circuit generates a frequency signal indicative of the number of rotations of the motor. This frequency signal is compared with the reproduced signal to detect the number of pulses of the reproduced signal contained in one period of the frequency signal. A reproducing area on the disk is detected by comparing the detected number of pulses with a predetermined value, since this number of pulses has a value corresponding to a radial position on the disk.

Abstract: An optical disk cutting apparatus comprises an exposure optical system for expanding an exposure laser beam and for modulating the exposure laser beam in response to a signal to be recorded, and a focus servo optical system for expanding a focus servo laser beam and for detecting a reflected beam from a master recording disk through a polarizing means, in which one of the exposure and focus-servo optical systems the laser beam of which has a wave length longer than that of the other one includes a focusing lens provided in a stage preceding the objective lens for focusing the expanded laser beam. Therefore, it is possible to make the respective focal positions of the exposure laser beam and the focus servo laser beam be substantially the same and to obtain a small aberration by means of the difference in refractive index between laser beams.

Abstract: An optical axis monitoring apparatus for monitoring a variation in the optical axis of light beams in an optical system. The apparatus includes a light source for generating a light beam to propagate along a first optical path. A diffraction optical element is disposed along the first optical path for diffracting the light beam into at least two orders of diffraction. At least one of the orders of diffraction propagates along the first optical path and another of the orders of diffraction propagates along a second optical path. A first monitoring element id disposed along the first optical path between the light source and the diffraction optical element for monitoring the first light beam and generating an incoming beam signal in response to light incident thereon. The incoming beam signal being indicative of the condition of the first light beam. A second monitoring element is disposed opposite the diffraction optical element from the first monitoring element and along said the second optical path.

Abstract: In an optical recording device, a record carrier (4) is scanned with an intensity-modulated write beam (13) to form an information pattern of optically detectable marks (8) on the record carrier (4). By means of a verification beam (13), which trails the write beam (14) at a fixed distance, the recorded information is read immediately after recording. The write beam (13) and the verification beam (14) are produced by the same radiation source (10) whose intensity is modulated in conformity with the information to be recorded. In order to eliminate the effect of this modulation in the read signal (Vl) obtained by means of the verification beam (14) a dividing circuit (51) divides the read signal (VI) by a signal (Vn) which is indicative of the instantaneous intensity of the radiation generated by the radiation source (10).

Abstract: A cutting apparatus is provided, in which a recording laser beam from a laser light source is ON/OFF-modulated by an optical modulating device on the basis of a square output signal in which a video FM wave signal is pulse width modulated by an audio FM wave signal thereby to form exposure pits on a master disc. This cutting apparatus includes a photodetector for receiving one portion of the recording laser beam irradiated on the master disc from the laser light source or a photodetector for receiving a reflected light of the recording laser beam irradiated on the master disc from the laser light source and which is reflected on the master disc. A detected output signal from the photodetector is supplied through a low-pass filter to a control circuit which controls an intensity of an output laser beam from the laser light source, and an offset of a source system line is adjusted so that a secondary higher harmonic component of a main carrier in the detected output from the photodetector is minimized.

Abstract: A record carrier having a disc-shaped substrate and a recording layer for optically writing information therein is disclosed which includes a guide groove extended in the rotational direction of the record carrier so that a plurality of revolutions of the guide groove are spaced apart from each other in radial directions of the record carrier, and a pit pattern provided between adjacent guide grooves, at positions arranged at intervals in the above rotational direction, for detecting the deviation of a light spot from the center line between adjacent guide grooves. The recording/reproducing operation for this record carrier is performed in such a manner that the first tracking error signal is detected from diffracted light from the guide groove, the second tracking error signal is detected from the pit pattern, and information is recorded in and reproduced from a land formed between adjacent guide grooves in a state that a tracking operation is performed using the first and second tracking error signals.

Abstract: Recording operations for an optical disk recorder are calibrated by adjusting recording power level (light intensity) such that a permissible crosstalk can be detected in adjacent erased tracks. Following the power level calibration, pulse duration or width is calibrated for a predetermined symmetry of recorded pulses along the calibration track. Various sequences and procedures are described. Calibration occurs at a plurality of radially spaced-apart tracks.

Abstract: In an optical pick-up apparatus, light beam from a laser beam source is reflected by an optical element and is incident onto a disk. The optical pick-up apparatus comprises a support structure disposed in the optical element and making a deforming direction of the optical element caused by the support structure parallel or perpendicular to a track direction of the disk mirrored on the optical element. The support structure supports end edge portions of the optical element approximately opposed to each other in the parallel or perpendicular direction with respect to the track direction of the disk mirrored on the optical disk.

Abstract: An optical type information recording medium has guide grooves for tracking formed in a concentric or spiral shape at a predetermined pitch; and a pre-format pit formed approximately midway between the guide grooves in the normal direction thereof and recording at least address information. The optical type information recording medium is constructed such that the predetermined pitch is a value ranged from 1.4 .mu.m to 2.0 .mu.m, and the depth of the pre-format pit is a value ranged from 0.46 .lambda./n to 0.58 .lambda./n where n shows the refractive index of a substrate of the medium and .lambda.

Abstract: In order to displace the light beam to a position on the disc determined by a given address code on an optically readable record carrier having information provided with address codes and recorded in substantially concentrical tracks for the purpose of accurate reading, the track pitch and the write velocity with which the information has been recorded on the relevant disc is determined prior to reading. The light beam is displaced from a position with a known address code successively across a given first and second number of tracks and the address code is read after each displacement. The track pitch and the write velocity are calculated from the data obtained so that the relation between the track number and the address code is accurately established.

Abstract: An information management system for writable optical discs, includes a disc (7) on which data (7a) and management information (7b) are recorded; an operating system (1) in which data in a read only optical disc can be managed by means of files, the operating system (1) having a read instruction (2) and a write instruction (3); read control portion (5) for changing the read instruction directed to the read only optical disc into a read address instruction directed to the disc (7), the read control portion (5) having modifying and loading portion (5b) for changing the management information (7b) into mutual information having a format of the read only optical disc; internal storage (5c) for storing the mutual information; and access changing portion (5d) responsive to the read instruction (2) for switching an access target such that the access target is the disc (7) when the read instruction (2) is directed to the data recorded on the disc ( 7), and that the access target is the internal storage (5c) when the

Abstract: An information storage device, has a container and at least two identical tical information carriers arranged coaxially inside the container and adapted for independent rotation in relation to each other. Each optical information carrier has a hollow cylindrical base made of a material transparent for laser radiation and a recording layer applied on this cylindrical base.

Abstract: A separation type optical pickup device for an optical information reading/writing apparatus using an optical recording medium. The device comprises a fixed optical system and a movable optical system. The fixed optical system is unmovable with respect to the recording medium and includes a laser beam source and has an opening through which the laser beam is output. The movable optical system is movable with respect to the recording medium and has an opening through which the laser beam is transmitted from the fixed optical system and includes a light guide for guiding the laser beam to the recording medium in a form of a convergent beam focussed on a surface of the recording medium. An expansible hollow member interconnects the fixed optical system and movable optical system in a state wherein the openings of the two systems as well as an optical path of the laser beam between the openings are enclosed by the hollow member.

Abstract: The present invention concerns an arrangement for reading an optically readable light reflective carrier on which data is stored in the form of the diffractive data elements which are deviations from a reference surface. The data elements each have a plurality of adjacent tracks located on the carrier with data elements being positioned on adjacent tracks. The system utilizes an illumination means for projecting a concentrated light spot onto the carrier in order to obtain diffraction of light along the entire length of each of the data elements with an optical arrangement collecting light reflected from a carrier in such a way that the light energy which is received when a projected light spot impinges on the reference surfaces greater than the light energy received when the projected light spot impinges on a data element.

Abstract: An optical storage medium is disclosed. In general, the storage medium includes a substrate, with a first, expansion layer, a second, reflective layer bonded to the first layer, and a third, retention layer bonded to the second layer, opposite the first layer. An opto-electronic system for recording data is also disclosed, along with a method of manufacture of the storage medium.

Abstract: An optical information processing method comprises a step of recording and/or reproducing information by irradiating a light beam to a periodically relatively moving record medium, detecting focusing and/or tracking servo signals and driving auto-focusing and/or auto-tracking means in accordance with the detected servo signals, a step of storing detected servo signals of at least one period of the movement of the medium, and a step of stopping the irradiation of the light beam to the medium and driving the auto-focusing and/or auto-tracking means in accordance with the stored ervo signals.

Abstract: The present invention relates to systems for reproducing signals, from a record whose engraved surface contains a recorded track in the form of an embossed print made of diffractive elements, representing the time variation of a pulse time modulated waveform. In accordance with the invention, there is provided a record and an optical read-out device wherein the relief elements carried by the record have a width in the order of the wavelength of the concentrated read-out radiation for determining a spatial variation in the diffracted energy emerging from the illuminated portion of the record, this variation being detected with a photo-electric detector.

Abstract: An improved coarse access and tracking servo system for use with an optical disk storage system is disclosed. Concentric servo tracks placed on the disk are readily distinguished from data tracks placed on the disk which may or may not be present on the disk depending upon the amount of information that has been written on the disk, i.e., how "full" the disk is with respect to its maximum capacity for storing data. A predetermined signal is embedded within each of the plurality of concentric servo tracks found on the disk. A radial strip or line, sufficiently long to always include at least one servo track, but also long enough to include data tracks, if any, on either side of the illuminated servo track is projected on the surface of the disk in order to detect the servo tracks.

Abstract: A photographic contact printing process is disclosed having application in the mass production of replicate video discs from a master disc, and other applications wherein it is desired to replicate micro-detail over a relatively large area. A problem with conventional contact printing from a mask to a photographic medium is one of maintaining intimate contact over a relatively large area since dust, dirt, etc., are almost impossible to completely eliminate in any practical manner. In accordance with the present invention, a contact printing process is provided wherein intimate contact is not necessary for making high quality contact prints. The present invention recognizes that in contact printing information from a master disc to a replicate disc, the contact printing process is significantly less sensitive to imperfect contact between the master disc and the replicate disc if one employs a replicate disc comprising a photosensitive material having a certain optical properties.

Abstract: An optical disk recording and reproducing apparatus is provided with an element in a servo system circuit, which element is provided high response characteristics to run out frequency. Output of the element is monitored for detecting whether a disk is defective.

Abstract: Disclosed is a system for optically recording information on a disc-shaped record carrier body along an information track, with the write spot being accurately guided in the radial and tangential directions. The record carrier body comprises a servo track formed by a constant and large number of servo areas per revolution of the servo track. In addition to a write spot, the write apparatus also projects a servo spot on the servo track. The tangential speed and the radial position of the servo spot relative to the servo track are determined from the modulated servo beam and used to correct the tangential speed and the radial position of the write spot, which is locked to the servo spot.

Abstract: The present invention relates to systems for reproducing signals, from a record whose engraved surface contains a recorded track in the form of an embossed print made of diffractive elements, representing the time variation of a pulse time modulated waveform. In accordance with the invention, there is provided a record and an optical read-out device wherein the relief elements carried by the record have a width in the order of the wavelength of the concentrated read-out radiation for determining a spatial variation in the diffracted energy emerging from the illuminated portion of the record, this variation being detected with photo-electric elements.

Abstract: A disk recording checking method in which recording is performed on a disk having radially different recording tracks each divided circumferentially into a plurality of sectors. The method employs a continuous writing device for continuously writing data onto a predetermined number of the sectors, and a continuous checking device for checking the data, while continuously reading the data from the predetermined number of the sectors. The method utilized checks both the number of errors in each code sequence and the total number of errors in each sector to determine if the data in the sector is valid.

Abstract: A record carrier having a disc-shaped substrate and a recording layer for optically writing information therein is disclosed which includes a guide groove extended in the rotational direction of the record carrier so that a plurality of revolutions of the guide groove are spaced apart from each other in radial directions of the record carrier, and a pit pattern provided between adjacent guide grooves, at positions arranged at intervals in the above rotational direction, for detecting the deviation of a light spot from the center line between adjacent guide grooves. The recording/reproducing operation for this record carrier is performed in such a manner that the first tracking error signal is detected from diffracted light from the guide groove, the second tracking error signal is detected from the pit pattern, and information is recorded in and reproduced from a land formed between adjacent guide grooves in a state that a tracking operation is performed using the first and second tracking error signals.

Abstract: An optical disk of the type including guide grooves is improved by regulating the width of the grooves, and thus the width of the adjacent land portion, in accordance with the type of information recorded at that part of the land.

Abstract: A pickup actuator includes a slider, an optical pickup unit, and at least one suspension arm extending from the slider for suspending the pickup unit. The pickup unit includes at least one bobbin surrounding a yoke plate, upon which a first coil is wound, and further transversely mounted coils attached to the first coil. The coils collectively control movement of the pickup unit in tracking, focusing and tilt directions thereof. A further bobbin connected to the slider surrounds the yoke plate and includes a further coil wound thereabout for driving the slider and the pickup unit radially of an associated optical disk.

Abstract: This invention provides an erasable optical disk, on which information is recorded and reproduced repeatedly through the irradiation of laser beams, and an optical information recording/reproduction apparatus which records and reproduces information on the erasable optical disk. In erasing and then recording information on the erasable optical disk by using an erasing laser beam and a recording/reproduction laser beam, respectively, the tracking of both laser beams on the same track is detected so as to prevent erroneous erasing. The apparatus uses the optical disk having a mark signal disposed between a sector identifier and a data field, which mark signal is capable of determining the presence of the erasing laser beam on an adjacent track on the erasable optical disk, and the apparatus reproduces and detects the mark signal by using the erasing laser beam.

Abstract: An optical information carrier includes a cylinder (1) with a recording layer (2) and bushings (3,4) located at butt ends of the hollow cylinder (1) and insulating the recording layer (2) from the environment. A method for erasing information recorded on the optical carrier uses a high-frequency electrical discharge produced inside the air-tight closed space (5) of the hollow cylinder (1). An optical storage device realizing the method includes an erasing unit (11) having a circuit for initiating a high-frequency discharge, which has electrodes (12,13) between which the optical carrier (10) is located so that the high-frequency discharge is initiated inside the closed air-tight space (5).

Abstract: A disk recording method in which recording is performed on a disklike recording medium having a radially coaxial or spiral recording track that is divided into a predetermined plural number of recording sectors each acting as a recording unit. A predetermined number of dedicated sectors are provided at a rear portion of the recording track so that the contents that are recorded in defective sectors of the recording sectors are alternatively assigned to the dedicated sectors.

Abstract: This specification discloses a card-like optical information recording medium comprising a card-like base body, and concentric circular or spiral information tracks provided on the base body and capable of optically recording and/or reproducing information thereon. The specification also discloses an apparatus for recording and/or reproducing information on such card-like optical information recording medium which comprises a turn table rotatable with the card-like medium being placed thereon, a clamp mechanism for positioning and fixing the card-like medium on the turn table, and an optical head for applying a light beam to the card-like medium while moving radially of the rotation, thereby effecting recording and/or reproduction of information concentrically or spirally.

Abstract: An optical head device for use in a disc player has a light beam generating and detecting unit for generating a light beam emerging therefrom and detecting a light beam coming thereto from the outside, an object lens driving unit for supporting an object lens and moving the same in both a first direction along an optical axis of the object lens and a second direction substantially perpendicular to the first direction, and a movable base member for supporting the light beam generating and detecting unit and the object lens driving unit both mounted thereon so that the light beam emerging from the light beam generating and detecting unit is incident through a predetermined path upon the object lens supported by the object lens driving unit. In an embodiment, the movable base member is formed into the shape of a plate, and the light beam generating and detecting unit and the object lens driving unit are mounted respectively on opposite surfaces of the movable base member.

Abstract: An optical information recording medium having a sharp front face of an optical information recording pit to thereby reduce jitter of a reproduced optical signal. The front and back end portions of a pit are made to have a sharp edge and a wider portion. In a cutting operation for an original medium used for mass production of medium, the light exposure amount to a photoresist on the original medium is controlled to increase it at the front and back edge portions of a pit.

Abstract: Disclosed is a system for optically recording information on a disc-shaped record carrier body along an information track, with the write spot being accurately guided in the radial and tangential directions. The record carrier body comprises a servo track formed by a constant and large number of servo areas per revolution of the servo track. In addition to a write spot, the write apparatus also projects a servo spot on the servo track. The tangential speed and the radial position of the servo spot relative to the servo track are determined from the modulated servo beam and used to correct the tangential speed and the radial position of the write spot, which is locked to the servo spot.

Abstract: The present invention relates to optical memories for storing data on the surface of an information-supporting medium including pre-formatted patterns. Such a memory may constitute a random access mass memory, and it may be read/write memory or it may be a write-once memory. The operations of writing to the memory and reading from the memory are based on the optical interaction which occurs at the point of impact of an incident optical beam which causes local changes in optical characteristics which are representative of the data when data is being written, and which produce optical modulation detectable by photoelectric means during data reading. The invention provides an optical memory in which the illumination mode common to reading data and to detecting pre-formatting patterns is modified in order to allow for operation in a standby mode or in order to delete areas reserved for storing data, for example.

Abstract: The present invention relates to systems for reproducing signals, from a record whose engraved surface contains a recorded track in the form of an embossed print made of diffractive elements, representing the time variation of a pulse time modulated waveform. In accordance with the invention, there is provided a record and an optical read-out device wherein the relief elements carried by the record have a width in the order of the wavelength of the concentrated read-out radiation for determining a spatial variation in the diffracted energy emerging from the illuminated portion of the record, this variation being detected with photo-electric elements.

Abstract: Apparatus for transferring data and other information between a data processing unit and a rectangular memory card which includes an optically readable data memory unit having a succession of substantially concentric data storage tracks thereon, the card also including at least one microelectronic component which stores further information. Such component is connected to connection points on the surface of the card. Data is read from the tracks of the memory unit by optical scanning during rotation of the card about the axis of symmetry of the memory unit, and information is transferred between the microelectronic component and the data processing unit by an information transfer unit which is coupled to the connection points on the card and to the data processing unit.

Abstract: A method and an apparatus for recording and reproducing information for use with an optical disk apparatus in which a pit edge recording method is used. According to the pit edge recording method, the leading edge and the trailing edge of a hole pit or a record domain generated during a recording operation are dealt with as information. During the recording, the recording pulse width and the recording power are corrected, and during the reproduction, the variation in the edge position is corrected.

Abstract: A scanning unit for an optical disc record carrier includes a radiation-sensitive detection system having a plurality of detection elements on which is formed a reflected image of the scanning spot on the track structure of the record carrier. A tracking error signal is derived by combining the output signals of detection elements situated on respective sides of a boundary line between two halves of the detection system, and comparing with each other the combined signals from both halves. Several different such tracking error signals are derived, for boundary lines having different orietations with respect to the direction of the track instantaneously being scanned. The tracking error signal corresponding to a boundary line most nearly parallel to the direction of such track will be of greatest amplitude, and is selected as the tracking error signal used for controlling the scanning unit to follow the center line of such track.

Abstract: An optical information carrier includes a cylinder (1) with a recording layer (2) and bushings (3,4) located at butt ends of the hollow cylinder (1) and insulating the recording layer (2) from the environment. A method for erasing information recorded on the optical carrier uses a high-frequency electrical discharge is produced inside the air-tight closed space (5) of the hollow cylinder (1). An optical storage device realizing the method includes an erasing unit (11) having a circuit for initiating a high-frequency discharge, which has electrodes (12,13) between which the optical carrier (10) is located so that the high-frequency discharge is initiated inside the closed air-tight space (5).

Abstract: An apparatus for reproducing data stored on a disc in a plurality of tracks connected in a continuous spiral or separated in concentric tracks.

Abstract: An erasable optical data storage medium including a substrate and a dual layer of a first material and a second material on the substrate. The dual layer is susceptible to expansion and contraction, to writing data thermally, to erasing data thermally and mechanically, and to reading data optically, the first material and the second material, respectively, being bonded together and remaining in the same physical state upon the expansion and relaxation of the dual layer. Methods and apparatus are also disclosed for recording data bits on the medium.

Abstract: Signal heads are displaced relative to a recording surface on a stationary recording medium having a separate surface on which visual data is recorded and displayed. Differential drive mechanism and adjustable resistor means effects signal head displacement along a predetermined path on the recording surface at a constant speed.

Abstract: A high density spiral track forming apparatus according to the present invention includes a linear motion mechanism for moving an optical recording system in a radial direction of a disk-shaped substrate, and a length measurement machine for detecting the distance travelled by the optical recording system in the radial direction of the substrate disk. The apparatus further includes a velocity computing device for detecting the travel velocity of the optical recording system according to the detected result of the length measurement instrument, and a velocity control device which detects the difference between the travel velocity of the optical recording system which is detected by the velocity computing device and a predetermined velocity, and controls the linear motion mechanism so as to eliminate that difference.