JP2001023186A - Digital system constant-current control circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a low-cost digital constant-current control circuit with further improved characteristics and with a simple configuration. SOLUTION: The digital system constant-current control circuit is composed of a subtraction circuit 3 for current deviation where an instruction voltage value is given from an upper-level controller 1, a digital integrator 4 for integrating a subtraction result digitally, an actuator drive circuit 6 for driving the actuator of a pickup based on the output of the integrator 4, a current detection amplifier for detecting the current of the actuator drive circuit for amplification, an A/D converter 11 for converting the output of the current detection amplifier from analog to digital and inputting it to the subtraction circuit for current deviation, gain switching judgment equipment 10-4 for switching the gain of the current detection amplifier according to the instruction voltage value in track-following servo, or according to a jump or seek status in track-following servo off, a gain switching circuit 5 for switching the gain of a digital integrator, and a circuit 2 for switching the instruction input range of the subtraction circuit for current deviation.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a constant current control circuit used for controlling an actuator for driving a pickup in a pickup control device represented by a CD-ROM drive, an MD drive, a magneto-optical disk drive and the like. Things.

[0002]

2. Description of the Related Art Generally, in a servo system for controlling a pickup for executing recording and reproduction on a target track with respect to a recording medium having a spiral recording track, in order to stabilize a frequency response characteristic of the servo system in particular, a constant value is required. Means for forming a minor loop by a current loop (acceleration loop) are known. In addition to the control using the constant current loop, an actuator driving method using constant voltage control is known. First, the concept and problems of the actuator driving method using constant voltage control will be described.

FIG. 4 is a conceptual diagram showing an actuator driving method by constant voltage control. In this actuator driving method, if the drive current of the actuator 101 to be controlled is I (s), and the displacement of the actuator 101 with respect to the drive current is X (s), the following equation (1) holds. In FIG. 4, reference numeral 102 denotes a resistance component of the actuator, and reference numeral 103 denotes an inductance of the actuator. X (s) / I (s ) = Ka / (Mt · s 2 + Dt · s + Kt) = (Ka / Kt) / {(Mt / Kt) · s 2 + (Dt / Kt) · s + 1} ···· (1) where s = jω = j · 2πf ｛ω: angular velocity (rad /
S), f: frequency (Hz)}, and the respective coefficients of equation (1) are as follows. Ka: torque constant Mt: actuator mass Dt: viscosity coefficient Kt: spring constant

Further, the driving current I (s) of the actuator 101 is defined by the following equation (2) by the command voltage V (s) and the inductance 103 and the resistance component 102 of the actuator 101. I (s) = V (s) / (Rc + Lc · s) (2) where Rc is an actuator resistance value and Lc is an actuator inductance. Therefore, the above (1)
From equation (2), the relational expression of the displacement X (s) of the actuator with respect to the command voltage V (s) is expressed by the following equation (3). X (s) / V (s) = (Ka / Kt) / [{(Mt / Kt) · s ² + (Dt / Kt) · s + 1} · (Rc + Lc · s)] (3) The primary resonance frequency f ₀ of the actuator is represented by the following equation (4). f ₀ = (1 / 2π) · (Kt / Mt) ^1/2 (4)

When the relational expression represented by the above expression (3) is conceptually expressed on the frequency axis, it becomes as shown by a thick curve A in FIG. In FIG. 6, the upper part of the vertical axis indicates the gain (dB), and the lower part indicates the phase (deg). Above the primary resonance frequency f _{0, the} frequency is attenuated by −40 dB / dec.
Decays by dB / dec. Further, the phase characteristic turns to -270 ° as shown by the thick curve C.

[0006] A problem with an actuator driving method according to the constant voltage control, when pulled to the target response frequency f _t as shown the response frequency of the system for example on FIG. 6, that is, when pulled up as indicated by the thick curve B In addition, the pole point P due to the actuators Rc and Lc approaches the zero cross frequency, so that the phase margin cannot be secured. In addition, Lc,
As Rc varies with ambient temperature and variations, the pole point position becomes more uncertain. Therefore, when the design of the system is advanced while leaving the problem of the pole point position, the system oscillates in an unexpected scene.

In order to avoid the problem of the actuator driving method by the constant voltage control, a control method using a constant current loop as shown in FIG. 5 is known. In this control method, the appearance of the pole point due to Rc and Lc of the actuator can be canceled. That is, as shown in FIG. 5, this control system is configured by incorporating a feedback system using a negative feedback amplifier 105 having a gain α and a feedback rate β.
The drive current I (s) is represented by the following equation (5). In FIG. 5, reference numeral 106 denotes a current detection resistor having a resistance value Rs. I (s) = V (s) / ｛(Rs + Rc + Lc · s) / α + β · Rs｝ V (s) / (β · Rs) (5) {(Rs + Rc + Lc · s)} α Therefore, the pole point is canceled by approximating the above equation (3) as shown in the following equation (6). X (s) / V (s) = (Ka / Kt) / [{(Mt / Kt) · s ² + (Dt / Kt) · s + 1} · (β · Rs)]・ ・ ・ ・ ・ ・ (6)

When the above equation (6) is conceptually expressed on the frequency axis, it becomes a curve A 'in FIG. Therefore, when raising the response frequency of the system up to f _t is as shown in curve B 'in FIG. 6, it is not necessary to consider the phase margin due to pole point. In this case, the phase characteristics are as shown by C '.

As described above, the actuator driving method based on the constant current control contributes to the stability of the system, and is generally realized by a configuration using analog elements as shown in FIG. . That is, in FIG.
Reference numeral 1 denotes a higher-level controller, which is not shown.The controller 201 forms a major loop by detecting position information of, for example, a pickup connected to an actuator, and performing position feedback control. . Reference numeral 202 denotes a D / A converter that outputs an operation amount (instruction value), and reference numeral 203 denotes an amplifier that calculates a current deviation.
This corresponds to the amplifier 105 having the gain α in the conceptual diagram shown in FIG. 204 is a driver, 205 is the inductance of the actuator, and 206 is the actuator itself. Reference numeral 207 denotes a current detection resistor. Reference numeral 208 denotes an amplifier that calculates a voltage value obtained from the current detection resistor 207 according to a feedback amount, and corresponds to a feedback ratio β in the conceptual diagram shown in FIG. It is.

[0010]

A constant current control circuit used in a conventional actuator driving method based on constant current control is:
It has no problem in function and can realize a desired operation, and is widely used. However, in order to further reduce the cost and improve the characteristics of the conventional constant current control circuit, there are the following problems.

First, the conventional constant current control circuit composed of analog elements has a problem that it is not suitable for a digital one chip using a CMOS process which is advantageous in reducing the cost of the system. External components such as a resistor and a capacitor have to be used, which raises the cost of the system and causes troubles in maintenance.

Secondly, in the conventional actuator driving method based on constant current control shown in FIG. 7, when digitizing except for the current detection amplifier, the dynamic range of the current detection amplifier must be considered. The reason for this is that in a system using an optical pickup typified by a magneto-optical disk controller, there are two cases: when the servo is turned on when the optical pickup is following the target track, and when the optical pickup jumps or seeks to the target track. This is because the dynamic range of the command voltage value from the host controller is greatly different, which immediately affects the dynamic range of the current detection amplifier.

Therefore, when the output of the current detection amplifier is A / D converted, when the input range of the A / D converter is determined so as not to be saturated even when the indicated voltage value is large, such as at the time of a track jump, Since the output value of the current detection amplifier at the time of track following cannot be converted finely, there is a problem that a sufficient degree of suppression (trackability to the target track) at the time of track following cannot be obtained. If the bit gradation of the A / D converter is increased, such a problem can be avoided. However, the cost of the A / D converter itself increases, and as a result, the required cost of the system is realized. become unable.

SUMMARY OF THE INVENTION The present invention has been made in order to solve the above-mentioned problems in the conventional actuator driving method using constant current control, and provides a low-cost digital constant current control circuit having a simple configuration and excellent characteristics. The purpose is to:

[0015]

SUMMARY OF THE INVENTION In order to solve the above problems, the present invention provides a control device for controlling a pickup for executing recording and reproduction on a target track on a recording medium having a spiral recording track. In the constant current control circuit used for the above, a subtraction circuit for a current deviation to which an instruction voltage value is given from a higher-order controller, a digital integrator for digitally integrating the subtraction result of the subtraction circuit for the current deviation, and a digital integrator based on the output of the digital integrator Drive circuit for driving the actuator of the pickup, a current detection amplifier for detecting and amplifying the current of the actuator drive circuit, A / D converting the output value of the current detection amplifier to subtract the current deviation An A / D converter for inputting to the circuit; The gain of the current detection amplifier according to a command voltage value given from the roller to the current deviation subtraction circuit, or according to a seek status or a track jump status given from the host controller when the track following servo of the pickup is turned off. Means for switching the gain of the digital integrator and the instruction input range of the current deviation subtraction circuit, and optimizes the input range of the A / D converter for A / D converting the output value of the current detection amplifier. So that
It constitutes a digital constant current control circuit.

In the digital constant current control circuit constructed as described above, when the track following servo of the pickup such as a track jump or seek state is off, or when the operation amount during the track following servo temporarily increases. Reduces the gain of the current detection amplifier and the gain of the digital integrator, and decreases the instruction input value of the current deviation subtraction circuit. On the other hand, during the track following servo, the gain of the current detection amplifier and the gain of the digital integrator are increased, and the instruction input value of the current deviation subtraction circuit is increased. As a result, even when the output value of the current detection amplifier is A / D converted with a small number of bits, the degree of suppression (trackability to the target track) at the time of track tracking servo can be secured. In addition, units other than the current detection amplifier can be integrated into a single digital chip including the host controller, and the cost of the system can be reduced.

[0017]

Next, an embodiment will be described. FIG. 1 is a block diagram showing an embodiment of a digital constant current control circuit according to the present invention. In FIG.
Reference numeral 1 denotes a host controller (not shown), which detects position information of, for example, a pickup connected to an actuator, and performs position feedback control. Reference numeral 2 denotes an instruction input range switching circuit for switching the instruction input range of the current deviation subtraction circuit at the subsequent stage, a multiplier for providing gains G1 and G2, and a result of the gain G1 or a result of the gain G2 among the multiplication results of the multipliers. And a register for holding the output of the selection circuit.

Reference numeral 3 denotes a current deviation subtraction circuit for subtracting an instruction input and a current deviation. Reference numeral 4 denotes a digital integrator for digitally integrating the subtraction result of the current deviation subtraction circuit 3. 5 with the digital integrator 4
Amplifier 105 with a gain of α in the constant current control circuit
It corresponds to. Reference numeral 5 denotes a gain switching circuit for switching the gain of the digital integrator 4, which includes multipliers 5-1 and 5-2 for providing a gain 1 / G1 and a gain 1 / G2, and a result of 1 / G1 among the multiplication results of the multiplier. Alternatively, it comprises a selection circuit 5-3 for selecting the result of 1 / G2. Numeral 6 denotes an actuator drive circuit for pickup, numeral 7 denotes an inductance of the actuator, numeral 8 denotes an actuator itself, and numeral 9 denotes a current detecting resistor.

Reference numeral 10 denotes an amplifier for calculating a current deviation, which corresponds to the feedback ratio β in the constant current control circuit shown in FIG. The current deviation operation amplifier 10 includes analog multipliers 10-1 and 10-2 for providing gains G1 and G2, and a multiplication result of the multiplier 10-1 or a multiplier 10-2 among the multiplication results of the analog multipliers. A selection circuit 10-3 for selecting a multiplication result of
The voltage value from the host controller 1 or the jump status and seek status information supplied from the host controller 1 are viewed, and the analog multiplier 10-1 or the
And a gain switching determiner 10-4 for generating an input signal to a selection circuit 10-3 for selecting a multiplication result of 10-2. 11 is a selection circuit 10-3 of the current deviation calculation amplifier 10
For A / D converting the current deviation signal output from
/ D converter.

FIG. 2 is a circuit diagram showing a specific configuration example of the current deviation operation amplifier 10 in the embodiment shown in FIG. In FIG. 2, reference numeral 21 denotes an upper controller bus 20.
The registers connected to are used to hold track jump and track seek statuses. In this configuration example, when the upper controller 1 writes "1" to the track jump bit or the track seek bit, the track following servo is turned off, and the upper controller 1 writes "0" to the track jump bit or the track seek bit. Sometimes, the track following servo is turned on. Reference numeral 22 denotes an instruction value register for writing a voltage instruction value from the host controller 1. Reference numeral 23 denotes a threshold value register for holding a threshold value of the voltage instruction value. Reference numeral 24 denotes the contents of a preset threshold register 23 and the indicated value register 22.
Are compared, and when the voltage indication value exceeds the threshold value, "1"
Is a digital comparison circuit that outputs. 25 is register 21
And an output of the comparison circuit 24 as an input.

Reference numerals 26, 27, 30, 32, and 33 denote resistors, reference numerals 28 and 29 denote analog switches, reference numeral 31 denotes a current detection resistor, reference numeral 34 denotes a current detection amplifier, and resistors 26, 27, analog switches 28, 29, and resistors.
At 30, the gain of the current detection amplifier 34 is set. That is, the analog multiplier 10- shown in FIG.
A gain corresponding to the gain G1 of 1 is shown.
The gain G of the analog multiplier 10-2 shown in FIG.
2 shows a gain corresponding to 2. And the OR circuit 25
Is "1", the analog switch 28 is turned on, the gain G1 set by the resistors 26 and 30 is selected, and
When the output of the R circuit 25 is "0", the analog switch 29 is turned on, and the gain G2 set by the resistors 27 and 30 is selected. In this configuration example, G1 (= 1) <G2.

Next, the operation of the embodiment shown in FIGS. 1 and 2 will be described with reference to the timing chart shown in FIG. FIG. 3 conceptually shows a track following operation or a jump operation. The instruction voltage is the operation amount itself from the host controller 1, and the output of the current detection amplifier is the selection circuit of the current deviation calculation amplifier 10 in FIG. 10-3, or the output level of the current detection amplifier 34 in FIG. 2, the current deviation is the output of the current deviation subtraction circuit 3 in FIG. 1, and the integrator output is the digital integrator 4 in FIG. Output. FIG. 3 shows each state from time point to and the gain G1 or G2 selected at that time point.

At the time,, is when the track following servo is being performed. At this time, the amplitude of the command voltage is originally small as indicated by the dotted line in the command voltage of FIG. However, the gain G2 is selected by the gain switching determiner 10-4 of the current deviation operation amplifier 10, and the instruction value input to the current deviation subtraction circuit 3 of FIG. 1 is changed by the instruction input range switching circuit 2 of FIG. The amplitude is apparently increased as shown by the solid line at the command voltage in FIG. 3. Similarly, the amplitude value of the output of the current detection amplifier 34 (the selection circuit 10-3 of the current deviation calculation amplifier 10) is also increased apparently as shown by the solid line, thereby making the A / D converter of FIG.
The bit truncation error due to 11 has been minimized. As post-processing when integrating the result of the current deviation, the gain switching circuit 5 of the digital integrator 4 in FIG.
By multiplying by 2, the range as the system is adjusted.

The time point is when the pickup is jumping (or seeking) with the track following servo off. However, the gain G1 is selected by the gain switching determiner 10-4 outputting "1", and the instruction value input to the current deviation subtraction circuit 3 via the instruction input range switching circuit 2 in FIG. , The amplitude remains unchanged. Similarly, the amplitude value of the output of the current detection amplifier 34 (selection circuit 10-3) has the same amplitude. In this way, signal saturation in the constant current control circuit loop is prevented.

The time point indicates a state where the amplitude of the command voltage happens to exceed the threshold value held in the threshold value register 23 in FIG. 2 during the track following servo. Also in this case, the gain G1 is selected by the gain switching determiner 10-4 outputting "1", and the instruction input to the current deviation subtraction circuit 3 via the instruction input range switching circuit 2 in FIG. The value is the same amplitude. Similarly, the amplitude value of the current detection amplifier 34 (selection circuit 10-3) has the same amplitude. In this way, signal saturation in the constant current control circuit loop is prevented.

[0026]

As described above with reference to the embodiments, according to the present invention, the gain of the current detection amplifier, the gain of the digital integrator, and the current deviation subtraction circuit are provided when the track following servo is off and the track following servo is performed. Is configured to be able to switch and change the instruction input range of
The input range of the / D converter can be optimized, and even if the output value of the current detection amplifier is A / D converted with a small number of bits, the degree of suppression during the track following servo can be secured. In addition, units other than the current detection amplifier can be integrated into a single digital chip, which can contribute to a reduction in system cost.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of a digital constant current control circuit according to the present invention.

FIG. 2 is a circuit configuration diagram showing a specific configuration example of a current deviation operation amplifier in the embodiment shown in FIG. 1;

FIG. 3 is a timing chart for explaining the operation of the embodiment shown in FIGS. 1 and 2;

FIG. 4 is a conceptual diagram showing a conventional actuator driving method of constant voltage control.

FIG. 5 is a conceptual diagram showing a conventional actuator driving method of constant current control.

FIG. 6 is a diagram showing frequency characteristics of the driving method shown in FIGS. 4 and 5;

7 is a diagram showing an actuator drive circuit in which the actuator drive method of constant current control shown in FIG. 5 is configured using analog elements.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Upper controller 2 Instruction input range switching circuit 3 Subtraction circuit for current deviation 4 Digital integrator 5 Gain switching circuit of digital integrator 5-1 and 5-2 Multiplier 5-3 Selection circuit 6 Pickup actuator drive circuit 7 Actuator drive Inductance 8 Actuator 9 Current detection resistor 10 Current deviation operation amplifier 10-1, 10-2 Analog multiplier 10-3 Selection circuit 10-4 Gain switching judgment device 20 Upper controller 21 Status holding register 22 Indication value register 23 Threshold value register 24 Digital comparison circuit 25 OR circuit 26, 27, 30, 32, 33 Resistance 28, 29 Analog switch 31 Current detection resistor 34 Current detection amplifier 25 A / D converter

Claims (1)

[Claims] 1. A constant current control circuit for use in a control device for controlling a pickup for executing recording and reproduction on a target track on a recording medium having a spiral recording track, wherein an instruction voltage value is supplied from a host controller. Current deviation subtraction circuit, a digital integrator for digitally integrating the subtraction result of the current deviation subtraction circuit, an actuator drive circuit for driving an actuator of a pickup based on an output of the digital integrator, and the actuator A current detection amplifier for detecting and amplifying a current of the drive circuit, an A / D converter for A / D converting an output value of the current detection amplifier and inputting the converted value to the current deviation subtraction circuit; Instruction to the current deviation subtraction circuit given by the host controller at the time of track following servo The gain of the current detection amplifier, the gain of the digital integrator, and the subtraction for the current deviation according to a voltage value or a seek status or a track jump status given by the host controller when the track following servo of the pickup is turned off. Means for switching respective input ranges of the circuit, wherein the input range of the A / D converter for A / D converting the output value of the current detection amplifier is optimized. Method Constant current control circuit.