Motor driver circuit for linear motor, positioning device using same, hard disk drive

Abstract

To reduce an area of a circuit for detecting counter-electromotive force.SOLUTION: A current detection circuit 212 generates a current detection signal VCS depending on a drive current of a linear motor 102 to be driven. A first amplifier AMP1 amplifies the current detection signal VCS. A second amplifier AMP2 multiplies a both-end voltage VM of the linear motor 102 by a gain less than 1, and outputs the resultant. A third amplifier AMP3 generates a counter-electromotive force detection signal VBEMF depending on a difference between output VA1 of the first amplifier AMP1 and output VA2 of the second amplifier AMP2.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a driver circuit for a linear motor. [Background technology]

[0002] Linear motors (linear actuators) are used in a variety of electronic devices and industrial machines to position objects. A voice coil motor is a type of linear motor that can control the position of a mover depending on the drive current supplied. The drive circuit of a voice coil motor performs feedback control to bring the current flowing through the voice coil motor closer to the target current that defines the target position.

[0003] An actuator driver that positions the head of a hard disk can switch between constant current control, which stabilizes the current at a target value, and control, which stabilizes the back electromotive force at a target value. Patent Document 1 discloses a circuit that detects back electromotive force by subtracting a voltage proportional to the motor current from the voltage between both ends of the motor. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 4707624 Summary of the Invention [Problem to be solved by the invention]

[0005] In applications such as hard disks, a 12V power supply voltage is used. Therefore, in the circuit described in Patent Document 1, the circuit block that detects back electromotive force must be configured with high-voltage elements that can withstand voltages higher than 12V. In particular, when the gain related to back electromotive force detection is made variable, attempting to switch the gain using high-voltage elements results in a large circuit area.

[0006] The present disclosure has been made in view of the above-mentioned problems, and one exemplary purpose of an embodiment thereof is to reduce the area of ​​a circuit that detects back electromotive force. [Means for solving the problem]

[0007] A motor driver circuit according to one embodiment of the present disclosure includes a current detection circuit that generates a current detection signal corresponding to the drive current of a motor to be driven, a first amplifier that amplifies the current detection signal, a second amplifier that multiplies the voltage across the motor by a gain smaller than 1 and outputs the result, and a third amplifier that generates a back electromotive force detection signal corresponding to the difference between the output of the first amplifier and the output of the second amplifier.

[0008] Any combination of the above elements, or mutual substitution of elements or expressions between methods, devices, systems, etc., are also valid aspects of the present invention or the present disclosure. Furthermore, the description in this section (Means for Solving the Problems) does not explain all essential features of the present invention, and therefore, subcombinations of the described features may also constitute the present invention. [Effects of the Invention]

[0009] According to an aspect of the present disclosure, the area of ​​a circuit for detecting back electromotive force can be reduced. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a block diagram of a positioning device including a motor driver circuit according to an embodiment. [Figure 2] FIG. 2 is an equivalent circuit diagram of the motor. [Figure 3] FIG. 3 is a block diagram of the back electromotive force detection circuit according to the first embodiment. [Figure 4] FIG. 4 is a block diagram of a back electromotive force detection circuit according to the second embodiment. [Figure 5] FIG. 5 is a circuit diagram showing an example of the configuration of a back electromotive force detection circuit. [Figure 6]FIG. 6 is a diagram showing a hard disk drive equipped with a motor driver circuit. DETAILED DESCRIPTION OF THE INVENTION

[0011] (Outline of the embodiment) A summary of some exemplary embodiments of the present disclosure is provided. This summary is intended to provide a simplified overview of some concepts of one or more embodiments in order to provide a basic understanding of the embodiments as a prelude to the more detailed description that follows. It is not intended to limit the scope of the invention or disclosure. This summary is not an exhaustive overview of all possible embodiments, and is not intended to identify key elements of all embodiments or to delineate the scope of some or all aspects. For convenience, the term "one embodiment" may refer to one embodiment (example or variant) or multiple embodiments (examples or variants) disclosed herein.

[0012] A motor driver circuit according to one embodiment includes a current detection circuit that generates a current detection signal corresponding to the drive current of the motor to be driven, a first amplifier that amplifies the current detection signal, a second amplifier that multiplies the voltage between both ends of the motor by a gain smaller than 1 and outputs the result, and a third amplifier that generates a back electromotive force detection signal corresponding to the difference between the output of the first amplifier and the output of the second amplifier.

[0013] A large voltage close to the power supply voltage can occur across the motor. If this large voltage is input to a subtraction amplifier, the subtraction amplifier must be constructed using high-voltage elements. In the above configuration, the second amplifier is provided to compress the DC bias contained in the voltage across the motor, thereby reducing the voltage input to the third amplifier, which is a subtraction amplifier. This allows the third amplifier to be constructed using low-voltage elements, thereby reducing the area of ​​the motor driver circuit.

[0014] In one embodiment, the second amplifier may include a first operational amplifier, a first resistor connected between a first input of the first operational amplifier and a first end of the motor, a second resistor connected between a second input of the first operational amplifier and a second end of the motor, a third resistor connected between the first input of the first operational amplifier and an output of the first operational amplifier, and a fourth resistor having one end connected to the second input of the first operational amplifier and the other end receiving a reference voltage.

[0015] In one embodiment, the third amplifier may include a second operational amplifier, a fifth resistor connected between a first input of the second operational amplifier and an output of the second amplifier, a sixth resistor connected between a second input of the second operational amplifier and an output of the first amplifier, a seventh resistor connected between the first input of the second operational amplifier and an output of the second operational amplifier, and an eighth resistor having one end connected to the second input of the second operational amplifier and the other end receiving a reference voltage.

[0016] In one embodiment, the motor may be a linear motor.

[0017] In one embodiment, the linear motor may be a voice coil motor.

[0018] In one embodiment, the motor driver circuit may be monolithically integrated on a single semiconductor substrate. "Monolithic integration" includes cases where all of the circuit components are formed on a semiconductor substrate, or where the main components of the circuit are integrated, and some resistors and capacitors for adjusting circuit constants may be provided outside the semiconductor substrate. By integrating the circuit on a single chip, the circuit area can be reduced and the characteristics of the circuit elements can be maintained uniformly.

[0019] A positioning device according to one embodiment includes a linear motor and any of the above-described motor driver circuits that drive the linear motor.

[0020] A hard disk drive according to one embodiment includes the above-described positioning device.

[0021] (Embodiment) Preferred embodiments will be described below with reference to the drawings. The same or equivalent components, parts, and processes shown in each drawing will be given the same reference numerals, and redundant explanations will be omitted as appropriate. Furthermore, the embodiments are examples and do not limit the disclosure and invention, and all features and combinations thereof described in the embodiments are not necessarily essential to the disclosure and invention.

[0022] In this specification, "a state in which component A is connected to component B" includes a case in which component A and component B are directly physically connected, and a case in which component A and component B are indirectly connected via other components that do not substantially affect the electrical connection state between them or impair the function or effect achieved by their combination.

[0023] Similarly, "a state in which component C is provided between component A and component B" includes not only cases in which components A and C, or components B and C, are directly connected, but also cases in which they are indirectly connected via other components that do not substantially affect the electrical connection state between them or impair the functions or effects achieved by their combination.

[0024] In addition, the vertical and horizontal axes of the waveform diagrams and time charts shown in this specification have been appropriately enlarged or reduced to facilitate understanding, and each waveform shown has also been simplified to facilitate understanding.

[0025] 1 is a block diagram of a positioning device 100 including a motor driver circuit 200 according to an embodiment. The positioning device 100 includes a linear motor 102, a host controller 104, and the motor driver circuit 200.

[0026] The host controller 104 comprehensively controls the positioning device 100. The host controller 104 is configured by, for example, a microcontroller, a field programmable gate array (FPGA), or an application specific integrated circuit (ASIC).

[0027] The motor driver circuit 200 receives a control command from the upper controller 104 and outputs a drive current I DRV is supplied to the motor 102. The motor 102 is, for example, a voice coil motor, and the rotor of the motor 102 is driven by a driving current I DRV The displacement is determined by the amount of

[0028] Next, we will explain the configuration of the motor driver circuit 200. Fig. 1 shows blocks related to speed control that stabilizes the speed of the linear motor 102 at a target value.

[0029] The motor driver circuit 200 includes a current detection circuit 210, a back electromotive force detection circuit 220, a feedback controller 230, an output stage 240, internal logic 250, and an interface circuit 260.

[0030] The current detection circuit 210 detects the drive current I DRV Current detection signal V according to CS Generate.

[0031] The back electromotive force detection circuit 220 outputs a current detection signal V CS and the voltage V across the motor 102 M Based on this, a back electromotive force detection signal V indicating the back electromotive force (BEMF) of the motor 102 is generated. BEMF The back EMF is proportional to the speed of the motor 102.

[0032] The internal logic 250 is a current command V REF In position control mode, the current command V REFvaries linearly with respect to the target position of the motor 102. In the speed control mode, the current command V REF is the back electromotive force detection signal V BEMF is generated so as to approach the speed command.

[0033] The interface circuit 260 is capable of communicating with the upper controller 104. The interface circuit 260 receives a current command V REF Alternatively, the information instructing the above may be received from the upper controller 104.

[0034] Current command V in speed control mode REF The calculation of may be performed in the internal logic 250. Alternatively, the interface circuit 260 may be used to transmit information on the back electromotive force to the upper controller 104, and the upper controller 104 may generate information instructing a current command so that the back electromotive force approaches the speed command, and transmit the information back to the internal logic 250.

[0035] The feedback controller 230 controls the current detection signal V CS is the current command V REF The voltage command V CTRL Generate.

[0036] The output stage 240 outputs a voltage command V CTRL For example, the output stage 240 generates a drive signal according to the voltage command V CTRL A voltage signal obtained by multiplying the voltage by a gain is applied to the motor 102.

[0037] Next, the speed control mode will be described in detail. As described above, in the speed control mode, it is necessary to detect information relating to the back electromotive force that indicates the speed of the motor 102. Therefore, the detection of the back electromotive force in the back electromotive force detection circuit 220 will be described.

[0038] 2 is an equivalent circuit diagram of the motor 102. The motor 102 is represented by a coil inductance L, a DC resistance r, and a voltage source 103. The voltage source 103 generates a back electromotive force e that is proportional to the rotation speed of the motor 102.

[0039] A constant drive current I is applied to the motor 102. DRV When it can be assumed that a current flows, the voltage (electromotive force) across the inductance L is zero, and the voltage drop across the resistance r is r×I DRV Therefore, the voltage V across the motor 102 M teeth, V M =I DRV ×re It is expressed as:

[0040] The back electromotive force detection circuit 220 outputs a current detection signal V CS By multiplying by the appropriate factor, I DRV ×r. Then, the voltage Vr between both ends of the motor 102 is generated. M By subtracting the voltage Vr from the BEMF Generate.

[0041] Returning to Fig. 1, the back electromotive force detection circuit 220 includes a calibration circuit 222, a first amplifier AMP1, a second amplifier AMP2, and a third amplifier AMP3.

[0042] The first amplifier AMP1 outputs the current detection signal V CS The second amplifier AMP2 multiplies the voltage between both ends of the linear motor 102 by a gain g2 smaller than 1 and outputs the result. For example, the gain g2 may be set to be smaller than 1 / 8.

[0043] The third amplifier AMP3 is the output V A1 and the output V of the second amplifier AMP2 A2 The back electromotive force detection signal V BEMF Generate.

[0044] The calibration circuit 222 is active in the calibration mode, and generates the back electromotive force detection signal V when the stator of the linear motor 102 is not moving, that is, when the back electromotive force e is zero. BEMF becomes zero. For example, the calibration circuit 222 adjusts the gain g1 of the first amplifier AMP1.

[0045] The above is the configuration of the motor driver circuit 200. Next, the operation thereof will be described.

[0046] In the calibration mode, the feedback by the feedback controller 230 is disabled, and the output stage 240 outputs a driving current I large enough to hold the mover of the linear motor 102 down against the mechanical end. DRV This causes the back electromotive force e to become zero.

[0047] The internal resistance of the linear motor 102 is r. In the calibration mode, the output V of the first amplifier AMP1 A1 is expressed by the following equation (1): A0 is the gain of the current detection circuit 212. V A1 =I DRV ×A0×g1…(1)

[0048] In the calibration mode, the back electromotive force is zero, so the voltage across the linear motor 102 is r×I DRV The output voltage V of the second amplifier AMP2 is A2 is expressed as equation (2). V A2 =g2×r×I DRV …(2)

[0049] In calibration mode, the back electromotive force detection signal V BEMF is expressed by equation (3). V BEMF =g3×(V A2 -V A1 ) …(3) g3 is the gain of the third amplifier AMP3.

[0050] In calibration mode, the back electromotive force detection signal V BEMF To make V zero, A2 =V A1 That is, the gain g1 is adjusted so that the following equation (4) holds true. I DRV ×A0×g1=g2×r×I DRV …(4)

[0051] That is, the adjusted gain g1 satisfies the formula (5). g1=g2×r / A0…(5)

[0052] In a normal operating state after calibration, it is assumed that a back electromotive force e is generated in the linear motor 102. At this time, the output V of the second amplifier AMP2 is A2 is expressed by equation (6). V A2 =g2×r×I DRV -e…(6)

[0053] At this time, the back electromotive force detection signal V BEMF is expressed by equation (7). V BEMF =g3×(V A2 -V A1 )=g3×(g2×r×I DRV -eI DRV ×A0×g1) …(7) Here, when g1 is adjusted by prior calibration to satisfy equation (5), the back electromotive force detection signal V BEMF is expressed by equation (8). V BEMF =g3×(g2×r×I DRV -eI DRV ×A0×g1)=-g3×e …(8)

[0054] In this way, the back electromotive force detection circuit 220 of the motor driver circuit 200 generates a back electromotive force detection signal V proportional to the back electromotive force e. BEMF can be generated.

[0055] The above is the operation of the motor driver circuit 200. Next, a specific example of the configuration of the back electromotive force detection circuit 220 will be described.

[0056] Example 1 FIG. 3 is a block diagram of the back electromotive force detection circuit 220 of FIG. 1. FIG. 3 shows the power supply voltage of each block and the withstand voltage of the transistors that make up each block. LV indicates that the block is made up of low-voltage elements, and HV indicates that the block is made up of high-voltage elements. For example, LV indicates an element that can operate in the range of 0 to 5 V, and HV indicates an element that can operate in the range of 5 to 15 V. In the first embodiment, the power supply voltage V DD is 1.5V.

[0057] The gain of the second amplifier AMP2 is, for example, g2 = 1 / 16. M When the voltage fluctuates between -10V and +10V, the output voltage V of the second amplifier AMP2 A2 In this case, the voltage across the motor is compressed to between -0.6V and 0.6V. high It consists of voltage-resistant elements.

[0058] The current detection circuit 210 detects the drive current I DRV The sense resistor Rs is connected to the path of the current detection signal V CS If the gain of this amplifier is 1, the gain A0 of the current detection circuit 210 is equal to Rs.

[0059] For example, Rs=0.22Ω, and the drive current I DRV If the current detection signal V is set to 0.78A to 4.55A, CS The current detection signal V can range from 0.17 to 1.0 V. CS The first amplifier AMP1 that amplifies is composed of low-voltage elements. The gain g1 of the first amplifier AMP1 is adjusted by calibration. The adjusted gain g1 is g1=g2×r / Rs The gain g1 depends on the internal resistance r of the motor 102. If r is assumed to be in the range of 2.1 to 12.2 Ω, the gain g1 is 0.6 to 3.48. The output voltage V of the first amplifier AMP1 A1 is about 0.6V.

[0060] The third amplifier AMP3 is configured with low-voltage elements and has a gain g3 of, for example, eight times.

[0061] Example 2 4 is a block diagram of a back electromotive force detection circuit 220 according to the second embodiment. DD is 5V. The gain of the second amplifier AMP2 is, for example, g2 = 1 / 4. The voltage V across the motor M When the voltage fluctuates between -9V and +9V, the output voltage V of the second amplifier AMP2 A2 In this case, the voltage across the motor is compressed to between -2.25V and 2.25V. high It consists of voltage-resistant elements.

[0062] Rs=0.22Ω, drive current I DRV If the current detection signal V is set to 0.73A to 4.26A, CS The current detection signal V can range from 0.16 to 0.94 V. CS The first amplifier AMP1 that amplifies is composed of low-voltage elements. The gain g1 of the first amplifier AMP1 is adjusted by calibration. The adjusted gain g1 is g1=g2×r / Rs The gain g1 depends on the internal resistance r of the motor 102. If r is assumed to be in the range of 2.1 to 12.2 Ω, the gain g1 is 2.4 to 13.92. The output voltage V of the first amplifier AMP1 A1 is 2.25 V, which is about four times that of Example 1.

[0063] The third amplifier AMP3 is configured with low-voltage elements and has a gain g3 that can be set to, for example, two times.

[0064] In the first embodiment, the gain g2 of the second amplifier AMP2 is 1 / 16. When the gain g2 is small, the detection accuracy of the back electromotive force is low. CS In the second embodiment, the gain g2 of the second amplifier AMP2 is 1 / 4, which is four times that of the first embodiment. This makes it difficult for the detection accuracy of the back electromotive force to be affected by errors in the current detection signal.

[0065] The above is the configuration of the back EMF detection circuit 220. In this back EMF detection circuit 220, the third amplifier AMP3 can be configured using low-voltage elements. This allows the area of ​​the back EMF detection circuit 220, and therefore the area of ​​the motor driver circuit 200, to be reduced.

[0066] There are cases where it is desired to make the gain g3 of the third amplifier AMP3 variable depending on the platform and the use of the linear motor 102. To switch the gain, a resistor network and multiple switches are required. When the third amplifier AMP3 is configured with high-voltage elements, the switches must be configured with high-voltage transistors, which causes the area of ​​the third amplifier AMP3 to increase.

[0067] 3 or 4, even if the gain of the third amplifier AMP3 is variable, the switch can be configured with a low-voltage transistor, thereby reducing the circuit area. Note that although the back-EMF detection circuit 220 includes the second amplifier AMP2 configured with a high-voltage element, the gain of the second amplifier AMP2 can be fixed, eliminating the need for a switch for gain switching, and therefore the effect of reducing the area of ​​the third amplifier AMP3 outweighs the area increase caused by the second amplifier AMP2.

[0068] 5 is a circuit diagram showing an example of the configuration of the back electromotive force detection circuit 220. The first amplifier AMP1 includes a third operational amplifier OA3, a ninth resistor R9, and a tenth resistor R10. A reference voltage V CMREFThe other end of the ninth resistor R9 is connected to the inverting input terminal of the third operational amplifier OA3. The tenth resistor R10 is connected between the inverting input terminal of the third operational amplifier OA3 and the output. The output voltage V of the first amplifier AMP1 A1 is expressed by equation (9). V A1 =V CS ×(R9+R10) / R9+V CMREF …(9)

[0069] The second amplifier AMP2 includes a first operational amplifier OA1 and a first resistor R1 to a fourth resistor R4. The first resistor R1 is connected between a first input (-) of the first operational amplifier OA1 and a first terminal (AOUT) of the linear motor 102. The second resistor R2 is connected between a second input (+) of the first operational amplifier OA1 and a second terminal (BOUT) of the linear motor 102. The third resistor R3 is connected between the first input (-) of the first operational amplifier OA1 and the output of the first operational amplifier OA1. The fourth resistor R4 has one end connected to the second input (+) of the first operational amplifier OA1 and the other end connected to a reference voltage V CMREF The output voltage V of the second amplifier AMP2 A2 is expressed by equation (10), where R1=R2 and R3=R4. V A2 =V M ×R3 / R1+V CMREF …(10)

[0070] The third amplifier AMP3 includes a second operational amplifier OA2 and a fifth resistor R5 to an eighth resistor R8, and is configured similarly to the second amplifier AMP2. When R5=R6 and R7=R8, the output voltage V BEMF is expressed by equation (11). V BEMF =(V A1 -V A2 )×R7 / R5+V CMREF …(11)

[0071] The above is an example of the configuration of the back electromotive force detection circuit 220.

[0072] (Application) 6 is a diagram showing a hard disk drive 900 equipped with a motor driver circuit 200. The hard disk drive 900 is equipped with a platter 902, a swing arm 904, a head 906, a spindle motor 910, a seek motor 912, and a motor driver circuit 920. The motor driver circuit 920 drives the spindle motor 910 and the seek motor 912.

[0073] The seek motor 912 is a voice coil motor. The motor driver circuit 200 according to the embodiment is built into a motor driver circuit 920 and drives the seek motor 912.

[0074] In this disclosure, the configuration or type of the linear motor to be driven is not particularly limited. For example, this disclosure can also be applied to driving a spring-return voice coil motor or other linear actuator. Alternatively, the motor to be driven may be a spindle motor.

[0075] The application of the positioning device 100 is not limited to hard disk drives, and it can also be applied to a positioning mechanism for a camera lens, etc. [Explanation of symbols]

[0076] 100 Positioning device 102 Linear motor 104 Upper controller 200 Motor driver circuit 210 Current detection circuit 220 Back electromotive force detection circuit 222 Calibration Circuit 230 Feedback Controller 240 output stage AMP1 First amplifier AMP2 Second amplifier AMP3 Third amplifier OA1 1st operational amplifier OA2 Second operational amplifier OA3 Third operational amplifier R1 First resistor R2 2nd resistor R3 3rd Resistance R4 4th Resistance R5 5th Resistance R6 6th Resistance R7 7th Resistance R8 8th Resistance R9 9th Resistance R10 10th Resistance

Claims

1. a current detection circuit including a sense resistor provided on a path of a drive current of a motor to be driven, and a current sense amplifier that converts a voltage drop across the sense resistor into a current detection signal; a first amplifier that amplifies the current detection signal output by the current sense amplifier; a second amplifier that multiplies the voltage between both ends of the motor by a gain smaller than 1 and outputs the result; a third amplifier that generates a back electromotive force detection signal according to a difference between an output of the first amplifier and an output of the second amplifier; Equipped with The motor driver circuit, wherein the second amplifier is composed of high-voltage elements, and the first amplifier and the third amplifier are composed of low-voltage elements.

2. The second amplifier is A first operational amplifier; a first resistor connected between a first input of the first operational amplifier and a first end of the motor; a second resistor connected between a second input of the first operational amplifier and a second end of the motor; a third resistor connected between the first input of the first operational amplifier and the output of the first operational amplifier; a fourth resistor having one end connected to the second input of the first operational amplifier and the other end receiving a reference voltage; 2. The motor driver circuit of claim 1, comprising:

3. The third amplifier is A second operational amplifier; a fifth resistor connected between the first input of the second operational amplifier and the output of the second amplifier; a sixth resistor connected between the second input of the second operational amplifier and the output of the first amplifier; a seventh resistor connected between the first input of the second operational amplifier and the output of the second operational amplifier; an eighth resistor having one end connected to the second input of the second operational amplifier and the other end receiving a reference voltage; 3. The motor driver circuit of claim 1, comprising:

4. 4. The motor driver circuit according to claim 1, wherein the motor is a linear motor.

5. 5. The motor driver circuit according to claim 4, wherein the linear motor is a voice coil motor.

6. 6. The motor driver circuit according to claim 1, which is monolithically integrated on a single semiconductor substrate.

7. A linear motor; a motor driver circuit according to any one of claims 1 to 6 for driving the linear motor; A positioning device comprising:

8. A hard disk drive comprising the positioning device according to claim 7.

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