WO2001033561A1

WO2001033561A1 - Device for reproducing and/or recording information on a disc shaped information carrier

Info

Publication number: WO2001033561A1
Application number: PCT/EP2000/010960
Authority: WO
Inventors: Yu Zhou; George Alois Leonie Leenknegt; Henrik Ladegaard
Original assignee: Koninklijke Philips Electronics N.V.
Priority date: 1999-11-04
Filing date: 2000-11-06
Publication date: 2001-05-10
Also published as: TW540030B

Abstract

The invention pertains to a device for reproducing and/or recording information on a rotating information carrier (1). The device comprises periodic disturbance compensation means (53) for generating a compensation signal for a periodic component in a control signal for a setting of the device. The periodic disturbance compensation means (53) are responsive to the error signal (RE), which error signal is an indication of a deviation of a desired setting. The periodic disturbance compensation means (53) generate a compensation signal uc(k) for a sample k complying with (I) wherein: φi is the ith harmonic of the periodic disturbance, w¿i?c(k), w¿i?s(k) are the weighting factors for the cosine and the sine term for the ith harmonic of the periodic disturbance, and T is the sampling time, the weighting factors being calculated as follows w¿i?s(k+1)=w¿i?s(k)+α¿i?e(k)sin(φikT+ζi) and wi?c¿(k+1)=w¿i?c(k)+α¿i?e(k)cos(φikT+ζi). Therein αi is a constant determining a learning rate for the i?th¿ harmonic and ζ¿i? is a phase.

Description

Device for reproducing and/or recording information on a disc shaped information earner

The invention relates to a device for reproducing and/or recording information on a disc shaped information earner

USP 4 616 276 descnbes a device for reproducing and/or recording an information earner The known device compnses an information earner in the form of a plurality of magnetic discs which are arranged on a common spindle One of the disc surfaces compnses servo-information for controlling the radial position of a set of transducers for transferring information to/from the information earner One of these transducers denves a position information signal from the servo information Signal processing means denve a first signal indicating a track index and a second signal (position error signal, PES) indicating the deviation of the set of transducers with respect to the track The device has a track following system, compnsing a servosystem and an actuator controlled by the servo system, to minimize the said deviation In addition the track follow g system compnses an adaptive control module which detects and compensates penodic vanations in the PES signal Such vanations may be caused by eccentricities in the information earner It is a disadvantage that the adaptive control module adapts relatively slowly to changes in the penodic vanations in the PES signal Such changes occur for example in a CLV or a QCLV system when the transducer is radially displaced and the rotational velocity of the record earner is changed In that case not only the frequency but also the amplitude of the penodic vanations changes

It is a purpose of the invention to provide a device for reproducing and/or recording an information earner having penodic disturbance compensation means which adapt relatively fast to vanations in the rotational velocity

A device according to the invention compnses means for rotating the information earner, means for reading a signal from the information earner, means for deriving an error signal which is an indication of a deviation of a desired setting, servo control means for generating a control signal in response to the error signal, - periodic disturbance compensation means, responsive to the error signal, for generating a compensation signal for a periodic component in the control signal, adding means for generating a sum signal which is an indication of the sum of the control signal and the compensation signal, correction means, responsive to the sum signal, for reducing the deviation in the desired setting, the periodic disturbance compensation means generating a compensation signal u_c(k) for a sample k complying with

u_c (k) = ∑{_W (k)cos(ω_ιkT) + w

wherein: ω, is the i^th harmonic of the periodic disturbance,

X(k), w (k) are the weighting factors for the cosine and the sine term for the i^th harmonic of the periodic disturbance, and

T is the sampling time, the weighting factors being calculated as follows

w^* (k + 1) = w,^Δ (k) + a,e(k)sm(_.ω,kT + φ, ), X, (0) = 0 and w,^r (k + 1) = w (k) + a,e(k)cos(ω,kT + φ, ), w,^f (0) - 0

wherein α, is a constant determining a learning rate for the i^th harmonic and φ, is a phase.

It was found by the inventors that a device according to the invention adapts relatively fast to changes in the periodic variations in the error signal. These and other aspects of the invention are descnbed in more detail with reference to the drawings. Therein:

Figure 1 schematically shows an embodiment of a device according to the invention,

Figure 2 shows a part of the device of Figure 1 in more detail, Figure 3 shows a view according to III of the part of Figure 2, Figure 4 shows another part of the device of Figure 1 in more detail, Figure 5 shows the error signal as a function of time both for the penodic disturbance compensation means switched on and switched off.

Figure 1 shows a device for reproducing and/or recording information on a rotating information earner 1 The device compnses means 12, 13 for rotating the information earner 1. The means for rotating are formed by a spmdle motor 12 which is controlled by spmdle motor controlling means 13. The spindle motor controlling means generate a rotation speed signal S_ω which is an indication for the rotation speed of the spindle motor 12. The device further compnses means 2 for reading a signal D1-D4 from the information earner 1 In casu the information earner 1 is an optical disc

The means 2 for reading the signal are formed by an opto-electncal transducer, which is shown in more detail in Figure 2. The transducer compnses a radiation source 20, such as a semi conductor laser, for generating a radiation beam 24. A lens 21, a beam splitter 22, and a focussing element 23 map the radiation beam 24 at a scanning spot 11, with which the information earner 1 is scanned. The transducer 2 further compnses detection means formed by an astigmatic element 25, and a four quadrant detector 26 for generating a read signal D1-D4. The read signal is a fourfold electncal signal. The components of the signal Dl, D2, D3, D4 correspond to the intensity of the light measured on four quadrants 26.1, 26.2, 26.3, 26.4 of the detector 26 as shown in Figure 3. A signal processor 3 denves from the read signal D1-D4 a first error signal RE which is an indication of the error in the radial position of the scanning point with respect to a track of the information earner 1. Also the signal processor 3 generates a second error signal, a focus error signal FE. The focus error signal FE is processed by a focus servo system 31, which in response generates a focus actuator control signal FA for focus actuator 27_A, 27_B. The signal processor 3 further generates an information signal L FO which represents the information read from the information earner 1. The device is provided with a servo controller 40, for example a PLO controller, see Figure 4, for generating a control signal RA for controlling the error in the radial position of the scanning point 11 in response to the error signal RE. The servo controller 40 forms part of a control system 4. The control system 4 compnses a vanable amplifier 41 receiving the radial error signal RE as its input, an offset compensation unit 42 for compensating a possible offset in the amplified radial error signal. The control system 4 also compnses correction means 43, 44 responsive to the control signal. In casu said means are formed by an actuator dnver 43 and a radial actuator 44 with radial actuator coils 28_A, 28β. The vanable amplifier 41, the offset compensation unit 42, the control signal generating means 40 and the actuator dnver 43 are coupled to a control unit 45 for controlling nonlinear control operations, such as start-up procedures, calibration, crash detection and recovenes The nonlinear control unit 45 is coupled to a microprocessor 6. The control system 4 further compnses sledge control means 46, compnsing a track counter 46 for determining a number of crossed tracks from the radial error signal, first subtracting means 47 for determining the difference between said number and a predetermined number of tracks ΔN_tr. The predetermined number of tracks AN* IS determined by the non-linear control means 45. An output of the first subtracting means 47 is coupled to a first input 48.1 of switching means 48 An output 48.3 of the switching means 48 is coupled to a sledge controller 49, here a Pi-controller which on its turn has an output coupled to a sledge dnver 50 which dnves a sledge 51 The switching means 48 has a second input 48.2 which is coupled via second subtracting means 52 to a sensor (not shown) which generates a signal X_a which is a measure for a deviation of the actuator 44. If the switching means 48 is in the switching mode indicated in the drawing, the latter signal X_a is selected as input signal for the sledge controller 49. In this mode, the scanning mode, the sledge controller 49 controls the sledge 51 so as to reduce the deviation of the actuator 44 The switching means 48 have a second mode in which the output of the first subtracting means 47 is selected as the input signal to the sledge controller 49. In this mode the sledge controller 49 controls the sledge 51 so as to access a predetermined track. The switching means 48, the sledge controllei 49 and the sledge dnver 50 are controlled by the non-lmear control unit 45.

The control system 4 further compnses penodic disturbance compensation means 53 for generating a compensation signal for a penodic component m the control signal, which are responsive to the error signal. An output of the servo controller 40 and an output of the compensation signal generating means 53 are connected to adding means 54 for adding the control signal and the compensation signal. The penodic disturbance compensation means 53 receive the signal S_ω representing the rotational velocity of the information earner 1. The periodic disturbance compensation means 53 generate a control signal u_c(k) for a sample k complying with

u_c(k) = ∑{w (k)cos(ω_lkT) + w! (k)&m(ω,kT)}

wherein:

is the i^th harmonic of the periodic disturbance, w (k), _w (k) are the weighting factors for the cosine and the sine term for the i^th harmonic of the periodic disturbance, and

T is the sampling time, the weighting factors being calculated as follows w' (k + 1) = u> (k) + αr_Ie(*) cos( fi>,*r + , ), w (0) = 0 and w;- (k + l) = w,⁵ (k) + α,e(&)sin(ω,£7/ + φ, ), w,^s (0) = 0 wherein ex, is a constant determining a learning rate for the i^th harmonic and φ, is a phase. The phase φ, is chosen such that the inequation:

is complied with. Therein:

Therein P(z) is the combined transfer function of the radial actuator 44 and its driver 43 and

C(z) is the transfer function of the actuator controller 40.

Preferably the value of φ, is chosen such that the left part of the inequation has a maximum value. The operation of the device of the invention was investigated by adding a periodic disturbance having a frequency of 110 Ηz to the radial control system. The control system was operated at a sampling rate of 7040 Ηz and the transient response of the radial control system was measured both with the periodic disturbance compensation means 53 switched on and switched off. In the former case a fast and stable adaptation to the periodic disturbance was obtained with a maximum learning rate oti equal to 3. In Figure 5 curve a and b respectively show the transient response with the periodic disturbance compensation means switched 53 on and for comparison with the periodic disturbance compensation means 53 switched off. From Figure 5 it is clear that in the former case the radial error signal RES is strongly reduced already after 1 revolution of the spindle motor 12.

Claims

CLAIMS:

1. Device for reproducing and/or recording information on a rotating information carrier (1), comprising means (12, 13) for rotating the information carrier (1), means (2) for reading a signal (D1-D4) from the information carrier (1), means (3) for deriving an error signal (RE) which is an indication of a deviation of a desired setting, servo control means (40) for generating a control signal (RA) in response to the enor signal (RE), periodic disturbance compensation means (53), responsive to the error signal (RE), for generating a compensation signal for a periodic component in the control signal, adding means (54) for generating a sum signal which is an indication of the sum of the control signal (RA) and the compensation signal (RC), correction means (43, 44), responsive to the sum signal, for reducing the deviation in the desired setting, - the periodic disturbance compensation means (53) generating a compensation signal u_c(k) for a sample k complying with

u_c(k) = ^{w'(k)cos(ω,kT) + w' (k)s (ω_lkT)}

1=1

wherein:

is the i^th harmonic of the periodic disturbance,

are the weighting factors for the cosine and the sine term for the i^th harmonic of the periodic disturbance, and T is the sampling time, the weighting factors being calculated as follows

w,^c (k + 1) = M (k) + a,e(k) cos(ω, kT + φ, )

and w_t' (k + l) = w; (k) + a,e(k)sm(ω,kT + φ, ) wherein , is a constant determining a learning rate for the i^th harmonic and φ, is a phase.

2. The device according to claim 1, characterized in that the phase φ, is chosen such that the inequation

is complied with.

3. The device according to claim 3, characterized in that the phase φ, is chosen such that left part of the inequation has a maximum value.

4. The device according to claim 1, 2 or 3, characterized in that the means (12, 13) for rotating the information carrier (1) provide a signal (S_ω) to the periodic disturbance compensation means (53) which indicates the rotational velocity of the information carrier (1).