Abstract: A mode of writing on a magnetic recording carrier (DISC) where the information is distributed over a plurality N of tracks, each track being associated with at least one reference zone (ZRP.sub.ij) including preamble information, absolute address information and fine-position information. According to the invention, the mode of writing is characterized in that the reference zone includes a first portion (GCP.sub.ij) comprising preamble and address information and a second portion (GDP.sub.ij) comprising fine-position information, the first portion being disposed and centered over the track of serial number j, while the second portion is offset by one-half of a track with respect to the center of that track and on the same side of that track. The invention is applicable to magnetooptical disk memories.

Abstract: A magnetic writing and optical reading head for a magnetic data carrier including at least one optical focusing device (SOI.sub.1, SOI.sub.1) for focusing a beam of light onto the carrier, and a magnetic writing transducer (TMI.sub.1, TMI.sub.2) disposed on the same rail (PI.sub.1, PI.sub.2) of the head as the optical device. According to the invention, the head is characterized in that the optical device and the transducer are disposed in the immediate vicinity of one another at a distance d less than the ratio of the difference between the width of the track L.sub.p and the diameter D of the beam of light produced by the device (SOI.sub.1, SOI.sub.2) to twice the sine of the maximum azimuth angle .psi..sub.M. The invention is applicable to magnetooptical disk memories.

Abstract: A DC motor drives a magnetic disk memory transducer head between a position proximate the disk periphery to an area on the disk where data are located during which time the head is lowered from an idle to a hovering position. During this time the motor is supplied with a current impulse having a predetermined polarity, amplitude and duration. The polarity of the current impulse is opposite to that of current applied to the motor while the head is being driven between a position beyond the disk periphery to the position proximate the disk periphery. The duration and amplitude of the current impulse are such that the motor angular velocity has a zero value at the completion of the current pulse. Thereafter, a ramping voltage having an average linear waveform is applied to the motor to prevent overshoot of the motor speed and prevent oscillation of the head relative to a face of the disk. The linear ramp current decreases to a zero value, at which time the motor has a constant, non-zero angular velocity.

Abstract: A magnetic disk memory is moved between a first position beyond the disk periphery to a second position proximate the disk periphery while the head is at an idle height above the disk face. The head is moved between the disk periphery and a third position at the edge of an area on the disk where data are located while the head is lowered and raised between the idle height and a hovering height above a face of the disk. An assembly carrying the head includes a radially extending arm, turned by a rotary DC motor. A continuous step excitation waveform is supplied to the motor as the head is driven between the first and second positions until the head arrives at one of the two positions. Each of the steps has a constant amplitude that differs from the immediately preceding step by a predetermined incremental value. All of the steps, except the last step, has the same predetermined duration.

Abstract: Data are written as transitions on plural tracks of a magnetic disc by a transducer which travels along an arcuate curve formed by an arm turning about an axis beyond the disc periphery. Transition positions are defined by the phase thereof relative to that of a reference indicator on a track of the disc. To align the transitions along a predetermined arcuate curve, a reference transition having a reference phase is written onto a given track. Other transitions of the second curve are written with a phase shift relative to the reference phase.

Abstract: A head is shifted relative to a magnetic disc for recorded information carried by plural concentric recording tracks on the disc. Addresses of the tracks are recorded on and read by a head from plural reference zones on the disc. The head is shifted from a starting track A to a destination track B by an electric motor. The motor is controlled so the head is accelerated from track A to track C and the head is decelerated when it reaches track C; track C being between tracks A and B. The motor is controlled by calculating an acceleration instruction for the head in response to addresses read by the head and by measuring the head acceleration. The instruction and measured accelerations are combined to derive an error indication that controls the motor.

Abstract: The relative speed of a movable head and a magnetic disc memory for data orded on a plurality of tracks, each having addresses written in a plurality of reference zones, is determined by reading the addresses read with the head at predetermined sampling times. The speed of the head is calculated as a function of the difference between the addresses read by the head and the interval between the sampling times.

Abstract: Cells of abutting magnetic disk tracks represent binary zeros and ones by having zero and one magnetic polarity transitions. The transitions in each cell for binary bits having the same value occur at the same relative place within the cell. A head positioned to straddle a pair of adjacent tracks simultaneously reads the magnetic transitions. Multiple successive cells along the lengths of the first and second abutting tracks provide only information to enable the head to be positioned to centrally straddle the abutting tracks. Aligned head positioning cells of abutting tracks have differing numbers of the transitions to represent the zero and one values. Even and odd numbered head positioning cells of a track respectively represent the zero and one value. Odd and even numbered head positioning cells of the abutting track respectively represent the one and zero binary values.

Abstract: Data, in the form of a sequence of binary bits of frequency F.sub.O, is detected by deriving a clock signal H of frequency F.sub.O in response to the sequence. A level transposing device responsive to the sequence and signal H derives a bi-level signal DEI. An integrating apparatus responds to DEI to derive a signal DEINT. A decision circuit responsive to DEINT determines the polarity of signal DEINT and derives binary data bits having values that are a function of the polarity. The direction and duration of charging current supplied to a pair of capacitors of the integrator are controlled as a function of the polarity and duration of each of the levels of signal DEI, so the capacitors are respectively charged in response to even and odd numbered bits. The integrator is reset to zero at the end of the integrating operation for each level and the capacitive integrating member is supplied with a charging current proportional to F.sub.O.

Abstract: The binary value of coded signals having opposite going transitions normally in the center of a bit cell, wherein the direction of the transition determines the binary value of the bit cell, is detected. The repetition rate of bit cells of a coded signal control the rate which a signal to be integrated is accumulated by an integrator. The integration duration is controlled by the length of the bit cell. The direction of integration is controlled by the direction of the center transition of each bit cell. In response to the amplitude of the accumulated signal at the end of the integration duration being greater or less than a reference amplitude, the binary value of the bit in the bit cell is determined. Integration is performed by first and second integrators respectively activated to accumulate the signal to be integrated during odd and even numbered bit cells. The first and second integrators are reset to zero during even and odd numbered bit cells, respectively.

Abstract: A phase comparator circuit arrangement is provided for controlling an electrical member on the basis of a control signal formed in accordance with the difference detected between a first waveform which is periodic and has a constant cyclic ratio, after it has locked on to a reference signal, and a second waveform which, after this locking on for which it serves as a reference, becomes non-periodic with a variable cyclic ratio for the purposes of exerting the said control. The circuit comprises a combination of a first bistable flip-flop circuit which receives the first and second waveforms respectively and which receives enabling voltages whose evolution is complementary between one input and the other. Means to subtract the waveform emitted by the first flip-flop circuit from the first waveform are provided to form the said signal for controlling the member.

Abstract: A system for positioning a displaceable member with respect to a reference conventionally uses a servo-mechanism having feedback position sensing and speed sensing loops connected to an input of the control path of the servo. Usually, the system operates in two successive phases:- a coarse positioning phase and a fine positioning phase. In the fine positioning phase, both loops are active. Nevertheless, if the reference tends to fluctuate, the accuracy of the final positioning may be less than acceptable. In a system according to this invention, an additional device is provided which, under a threshold value of the output of the position difference sensor, disconnects the speed difference sensor and inserts in the single remaining loop series correcting networks which, in addition to ensuring improved accuracy of the final positioning, also ensures an accurate follow-up of the fluctuations of the reference.