JP2009162673A - Position detector and method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a highly precise position detector for correcting the offset of an output signal. <P>SOLUTION: This position detector 100 detects the position of a measuring object based on two-phase output signals 1a and 1b output according to variation in position of the measuring object. The position detector 100 comprises analog-digital converting means 2a and 2b for digital-converting the two-phase output signals 1a and 1b and outputting the digital signals, a correcting means 50 for correcting the offset of the digital signals by calculating the center position of a Lissajou's waveform using at least three of the points on the Lissajou's waveform created by the digital signals, and a digital arithmetic means 3 for calculating the position of the measuring object using the signals corrected by the correcting means 50. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a position detection device, and more particularly to a position detection device including a correction unit that corrects an offset of an output signal.

Conventionally, there is a correction method for converting an output signal (periodic signal) generated in accordance with a change in the position or angle of an object to be measured into a digital signal and correcting the offset of the output signal from the digital signal. In JP-A-8-145719 (Patent Document 1), the maximum and minimum values of the output signal are detected by moving the object to be measured at a sufficiently slow speed with respect to the sampling period of the digital calculation, and the amplitude is determined from the width. And offset correction from the midpoint is disclosed.
JP-A-8-145719

    However, analog-digital conversion and digital calculation are performed at certain time intervals (sampling periods). In order to obtain the true maximum and minimum values in the output signal, it is necessary to move the object to be measured sufficiently slowly with respect to a predetermined sampling period and acquire the analog-digital conversion value in detail with respect to the period of the periodic signal. It was. If such control is not performed, the true maximum value and the minimum value cannot be detected, and the detection accuracy deteriorates.

    Thus, in the conventional technique, the object to be measured must be moved slowly, which takes time. For this reason, an offset correction value is obtained from the maximum value and the minimum value in a limited range, and this correction value is summarized in the entire use range. As a result, in applications where high accuracy is required, sufficient accuracy may not be obtained over the entire range used.

    As a countermeasure, there is a method in which the entire use range is divided into several sections and a correction value is provided for each section. However, this method is cumbersome to use because it is necessary to measure the correction in each section in advance and to constantly monitor the current position during operation and switch the correction value.

    Therefore, the present invention provides a highly accurate position detection apparatus and position detection method with a simple configuration.

    A position detection apparatus according to one aspect of the present invention is a position detection apparatus that detects the position of an object to be measured based on a two-phase output signal that is output in accordance with a change in the position of the object to be measured. By calculating the center position of the Lissajous waveform by using at least three points on the Lissajous waveform generated by the digital signal and analog-digital converting means for digitally converting the two-phase output signal and outputting the digital signal Correction means for correcting the offset of the digital signal, and digital calculation means for calculating the position of the object to be measured using the signal corrected by the correction means.

  A position detection method according to another aspect of the present invention is a position detection method for detecting the position of the object to be measured based on a two-phase output signal output in accordance with a change in the position of the object to be measured. Capturing the amplitude of the first two-phase output signal, the amplitude of the second two-phase output signal, and the amplitude of the third two-phase output signal from the two-phase output signal; and the two-phase output signal On the Lissajous waveform, passing through the midpoint of the first position obtained from the amplitude of the first two-phase output signal and the second position obtained from the amplitude of the second two-phase output signal, and Obtaining a first perpendicular perpendicular to a first straight line connecting the first position and the second position; and on the Lissajous waveform of the two-phase output signal, the second two-phase output signal From the second position obtained from the amplitude and the amplitude of the third two-phase output signal A second perpendicular line passing through a midpoint of the third position and perpendicular to a second straight line connecting the second position and the third position; the first perpendicular line and the first perpendicular line; Obtaining an intersection position with a second perpendicular, correcting the offset of the two-phase output signal by subtracting the difference between the intersection position and the origin position from the two-phase output signal; Detecting the position of the object to be measured using a correction value obtained by correcting the offset.

  Other objects and features of the present invention are illustrated in the following examples.

  ADVANTAGE OF THE INVENTION According to this invention, a highly accurate position detection apparatus and a position detection method can be provided.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

    The present embodiment relates to a position detection apparatus and a position detection method for correcting an offset of an output signal generated according to a change in the position of an object to be measured. Here, the term “change in position” includes not only linear displacement but also other displacement such as angular displacement.

    In this embodiment, first, the reason why the offset error of the output signal affects the accuracy of the position detection device will be described.

    In general, the error of the output signal from the position detection device includes an amplitude error and an offset error. In the position detection device, in order to obtain position or angle information by dividing two output signals whose phases are different from each other by 90 °, it is necessary to obtain an amplitude ratio of the two output signals. The amplitude of the output signal is detected in the same way for the two output signals due to the configuration of the detection means. Therefore, the amplitude of the output signal tends to increase or decrease in the same way for both output signals. For this reason, when the fluctuation (error) of the output signal from the position detection device is only the amplitude, this fluctuation (error) is canceled when obtaining the amplitude ratio of the two output signals, and the output signal accuracy is greatly affected. do not do.

    However, when there is an offset variation in the output signal from the position detection device, there is no canceling effect like the amplitude variation. For this reason, the offset fluctuation has a great influence on the accuracy of the output signal.

    In the present embodiment, as an example, a position detection apparatus used for a servo track writer of a hard disk will be described. However, the position detection device of the present invention is not limited to this, and may be used for other purposes.

    First, the function of the servo track writer will be briefly described. FIG. 8 shows an example of the structure of the servo track writer in the hard disk drive.

    Reference numeral 10 denotes a medium (disk). The surface of the medium 10 is coated with a magnetic material, and a servo track signal 15 that is magnetically used as a position signal reference is written in advance at the time of manufacture. The medium 10 is rotated by a spindle motor (not shown).

    11 is a swing arm. The swing arm 11 is configured to be movable in the radial direction of the medium 10 by an actuator (not shown). Reference numeral 12 denotes a magnetic head. The magnetic head 12 is attached to the tip of the swing arm 11. While the swing arm 11 is moving, the magnetic head 12 reads information recorded on the medium 10 and writes information to the medium 10.

    Reference numeral 13 denotes a push pin. As shown in FIG. 8, the swing arm 11 is pressed by a push pin 13 during servo track writing. For this reason, the swing arm 11 moves integrally with the push pin 13.

    Reference numeral 14 denotes a positioning mechanism including an encoder and a motor. For high-precision positioning, for example, an encoder that outputs a signal of 81000 cycles per rotation is used.

    The positioning mechanism 14 is configured to be rotatable on the same axis as the center of rotation of the swing arm 11 that is the object to be measured. Further, the positioning mechanism 14 divides the output signal of the encoder by a control device (not shown) so that positioning can be performed with a finer resolution than the output signal. When the position detection device of this embodiment is used for a servo track writer of a hard disk drive, the position detection device is included in the positioning mechanism 14.

    The servo track writer of the hard disk drive repeatedly positions the swing arm 11 and the magnetic head 12 in the radial direction of the medium 10 in micro steps by the positioning mechanism 14. The servo track writer writes the servo track signal 15 to the medium 10 while repeating this. Once the servo track signal 15 is written, the hard disk is positioned with reference to this track, and data is written and read.

    In order to improve the capacity of the hard disk, it is important to reduce the interval (track pitch) between servo tracks. Furthermore, a constant track pitch is required to improve the capacity.

    When the track pitch is narrowed, positioning is performed several times during one cycle of the encoder. Even in this case, in order to make the track pitch constant, linearity is required when the output signal (periodic signal) of the encoder is divided. That is, a division value that is exactly proportional to the rotation angle of the motor is required.

    Next, linearity at the time of dividing the output signal of the encoder will be described.

    FIG. 9 shows the relationship between the encoder output signal (periodic signal) and the division result. In FIG. 9, the encoder output signal 1a and the output signal 1b are 90 ° out of phase with each other. The upper waveform in FIG. 9 is the amplitude-time characteristic of the output signal. The output signal 1a has a vertically symmetrical waveform with respect to the center position indicated by the broken line. On the other hand, the output signal 1b is shifted upward with respect to the center position indicated by the broken line, and does not have a vertically symmetrical waveform. This is because the output signal 1b includes an offset component.

    The division result obtained by dividing the encoder output signals 1a and 1b is shown in the lower part of FIG. Line 16 is the result when there is no offset, and line 17 is the result when there is an offset. The division result is ideally a straight line like the line 16. However, as described above, when there is an offset in the output signal 1b of the encoder, the line 17 fluctuates so as to wave as the position changes. That is, if the output signal contains an offset component, the linearity of the signal cannot be ensured.

    If the division result does not become a straight line as shown by the line 17, the track pitch (inter-track interval) at the time of servo writing is not constant, and the performance of the hard disk cannot be ensured. For this reason, it is necessary to remove the offset in the output signal of the encoder so that the division result is a straight line as shown by the line 16.

    Next, the configuration of the position detection device in the present embodiment will be described. FIG. 1 is a schematic diagram of a position detection apparatus 100 in the present embodiment.

  In FIG. 1, 1a and 1b are two-phase output signals output from a detection means (not shown). Examples of the detection means include an encoder, but are not limited thereto. The output signal output from the detection means is a periodic signal, and a signal having a predetermined period is repeatedly output. The output signal as the periodic signal is a sine wave signal in this embodiment, but is not limited to this.

  Reference numerals 2a and 2b denote analog-digital conversion means. The analog-digital conversion means 2a, 2b receives an analog signal, converts the analog signal into a digital signal, and outputs the converted digital signal. In this embodiment, the analog-digital conversion means 2a converts the output signal 1a, which is an analog signal, into a digital signal. Similarly, the analog-digital conversion means 2b converts the output signal 1b, which is an analog signal, into a digital signal.

  Reference numeral 50 denotes correction means. The correcting means 50 corrects the offset of the digital signal by calculating the center position of the Lissajous waveform using at least three points on the Lissajous waveform generated by the digital signal. That is, the correction means 50 is provided for correcting the offset of the two-phase output signals 1a and 1b.

  As described above, in this embodiment, the Lissajous waveform is drawn 81000 times while the encoder makes one revolution. The offset of the output signal varies depending on the rotational position of the encoder. For this reason, the three points on the Lissajous waveform are desirably taken during one period of the Lissajous waveform, but may be in the vicinity of the period.

If the position of the encoder changes, the offset of the output signal also changes. For this reason, the correction means 50 repeats the offset correction according to the position of the encoder as the encoder rotates.

  Reference numeral 51 denotes an offset calculation means. The offset calculation means 51 calculates the center position of the Lissajous waveform using the three points at the first position, the second position, and the third position on the Lissajous waveform. Specifically, the offset calculation means 51 passes through the midpoint of the first straight line connecting the first position and the second position on the Lissajous waveform and is perpendicular to the first straight line. Ask for. Similarly, a second perpendicular line passing through the midpoint of the second straight line connecting the second position and the third position on the Lissajous waveform and perpendicular to the second straight line is obtained. Then, the intersection position between the first perpendicular line and the second perpendicular line is calculated as the center position.

    As will be described later, the offset calculation means 51 can also calculate a plurality of intersection positions and set an average value of the plurality of intersection positions as the center position.

  52a and 52b are subtraction means. The subtracting means 52a and 52b subtract the difference between the center position calculated by the offset calculating means 51 and the origin position from the digital signals output from the analog / digital converting means 2a and 2b. Here, the origin position is the center position of the Lissajous waveform generated based on ideal output signals 1a and 1b having no offset.

    The correcting means 50 of this embodiment is composed of an offset calculating means 51 and subtracting means 52a and 52b. However, it is not limited to such a configuration, and other configurations may be used.

  Reference numeral 3 denotes digital arithmetic means. The digital calculation means 3 uses the digital signal offset-corrected by the correction means 50 to calculate the position of the object to be measured. The digital calculation means 3 calculates the position of the object to be measured with a period finer than the period of the output signals 1a and 1b from the digitally converted signal.

    Next, the waveforms of the output signals 1a and 1b output from the detection means will be described.

    FIG. 2A shows the amplitude-time characteristics of the output signals 1a and 1b. In this figure, the output signals 1a and 1b are both ideal periodic signals (sine wave signals) having no offset. Further, the phases of the output signals 1a and 1b are different from each other by 90 °.

    FIG. 2B is a waveform diagram when the vertical axis represents the amplitude (signal intensity) of the output signal 1a and the horizontal axis represents the amplitude (signal intensity) of the output signal 1b. Such a waveform is called a Lissajous waveform. The output signals 1a and 1b make one rotation on the circumference of the Lissajous waveform 4 when changed by one period in FIG.

    In this embodiment, when the encoder is rotated once, a sine wave having 81000 periods is output as the output signal of FIG. Further, as the Lissajous waveform 4 in FIG. 2B, a circle of 81000 times is drawn.

    As shown in FIG. 2B, when the output signals 1a and 1b are ideal waveforms, the Lissajous waveform 4 draws a circle with the origin position (0, 0) as the center position.

However, when there is an offset in the output signals 1a and 1b, the center position of the Lissajous waveform 4 deviates and indicates a position (x ₀ , y ₀ ) different from the origin position ( ₀ , ₀ ). Therefore, if the position (x ₀ , y ₀ ) is corrected so as to be the origin position, the offset included in the output signals 1a and 1b can be removed.

    Next, a specific procedure for offset correction in the present embodiment will be described. FIG. 3 shows the relationship between the position on the Lissajous waveform (coordinates on the Lissajous waveform) and the center position (coordinates of the center point).

The offset correction in the present embodiment is performed by obtaining the center position (x ₀ , y ₀ ) of the Lissajous waveform 4 using the position on the circumference of the Lissajous waveform 4. Hereinafter, a method for obtaining the center position will be described.

In FIG. 3, three positions are specified on the circumference of the Lissajous waveform 4. The coordinates at the positions of these three points are defined as a first position (x ₁ , y ₁ ), a second position (x ₂ , y ₂ ), and a third position (x ₃ , y ₃ ), respectively. First, the first position (x ₁ , y ₁ ) and the second position (x ₂ , y ₂ ) are connected by the first straight line 5. Then, a first perpendicular line 6 passing through the midpoint between the first position (x ₁ , y ₁ ) and the second position (x ₂ , y ₂ ) and perpendicular to the first straight line 5 is drawn. . Similarly, the second position (x ₂ , y ₂ ) and the third position (x ₃ , y ₃ ) are connected by the second straight line 7. Then, a second perpendicular line 8 that passes through the midpoint between the second position (x ₂ , y ₂ ) and the third position (x ₃ , y ₃ ) and intersects the second straight line 7 perpendicularly is drawn. .

As shown in FIG. 3, the first perpendicular line 6 and the second perpendicular line 8 intersect at an intersection (x ₀ , y ₀ ). Here, assuming that the Lissajous waveform 4 is an ideal circle, the intersection of the first perpendicular 6 and the second perpendicular 8 obtained as described above is the center position of the Lissajous waveform 4. For this reason, calculating the intersection of the first perpendicular line 6 and the second perpendicular line 8 calculates the center position of the Lissajous waveform 4.

When the output signals 1a and 1b include an offset, the center position (x ₀ , y ₀ ) of the Lissajous waveform 4 obtained as the intersection position of the first perpendicular line 6 and the second perpendicular line 8 is the origin position (0 , 0).
The difference between the center position (x ₀ , y ₀ ) and the origin position (0, 0) corresponds to the offset of the output signals 1a and 1b.

For this reason, in this embodiment, the offset correction value is obtained from the difference between the center position (x ₀ , y ₀ ) and the origin position (0, 0). That is, the difference between the center position (intersection position) and the origin position is subtracted from the two-phase output signal. By such a method, the center position (x ₀ , y ₀ ) of the Lissajous waveform 4 is corrected so as to be the origin position (0, 0). The offset correction in the present embodiment can be executed by obtaining at least three points on the Lissajous waveform 4.

Next, how to obtain the perpendicular will be described. Based on the information of two points of the first position (x ₁ , y ₁ ) and the second position (x ₂ , y ₂ ) on the Lissajous waveform 4, the first perpendicular line 6 is obtained as follows.

FIG. 4 is a diagram illustrating how to obtain the first perpendicular 6 that passes through the midpoint between the first position (x ₁ , y ₁ ) and the second position (x ₂ , y ₂ ). This figure extracts the relationship between the 1st straight line 5 and the 1st perpendicular line 6 of FIG.

Let the point on the first perpendicular 6 be (x, y). The first perpendicular line 6 has the same distance from the two points of the first position (x ₁ , y ₁ ) and the second position (x ₂ , y ₂ ). That is, the lengths of the dotted lines shown in FIG. 4 are equal at any point (x, y) on the vertical line 6.

A distance d ₁ from the first position (x ₁ , y ₁ ) to an arbitrary point (x, y) on the first perpendicular 6 is obtained by the formula (1) by the square root of the sum of squares of the differences. .

d ₁ = ((x ₁ −x) ² + (y ₁ −y) ² ) ^1/2 (1)
Similarly, a distance d ₂ from the _second position (x ₂ , y ₂ ) to an arbitrary point (x, y) on the first perpendicular 6 is obtained by Expression (2).

d ₂ = ((x ₂ −x) ² + (y ₂ −y) ² ) ^1/2 (2)
Here, the distances d ₁ and d ₂ are equal to each other. For this reason, the relationship of Formula (3) is established.

((X ₁ −x) ² + (y ₁ −y) ² ) ^1/2
= ((X ₂ -x) ² + (y ₂ -y) ² ) ^1/2 (3)
When the relational expression of x and y is obtained from Expression (3), Expression (4) can be derived.

2 (y ₂ -y ₁ ) y
= 2 (x ₁ −x ₂ ) x + x ₂ ² + y ₂ ² −x ₁ ² −y ₁ ² (4)
_{Here, x 1, y 1, x} 2, y 2 is a constant. For this reason, it becomes a linear equation regarding x and y, that is, a linear equation. When the constant portion is represented by a ₁ and b _1, it is represented by Expression (5).

y = a ₁ x + b ₁ (5)
Here, a ₁ = (x ₁ −x ₂ ) / (y ₂ −y ₁ ),
b ₁ = (x ₂ ² + y ₂ ² −x ₁ ² −y ₁ ² ) / 2 (y ₂ −y ₁ ).

Similarly, the second perpendicular line 8 is also expressed as Equation (6), where the constant portions are a ₂ and b ₂ .

y = a ₂ x + b ₂ (6)
_{Here, a 2 = (x 2 -x} 3) / (y 3 -y 2),
b ₂ = (x ₃ ² + y ₃ ² −x ₂ ² −y ₂ ² ) / 2 (y ₃ −y ₂ ).

As described above, the intersection position (x ₀ , y ₀ ) between the first perpendicular line 6 and the second perpendicular line 8 can be calculated from the two linear equations of the formulas (5) and (6). As shown, it can be determined uniquely.

_{x 0 = (b 2 -b 1} ) / (a 1 -a 2) ... (7)
_{y 0 = a 2 (b 2} -b 1) / (a 1 -a 2) + b 2 ... (8)
Similarly, even if three or more perpendicular lines are used, one intersection is obtained by a combination of two perpendicular lines.

    The Lissajous waveform 4 may have an error with respect to a perfect circle. In some cases, the value may deviate from the ideal Lissajous waveform due to noise. For this reason, the intersection obtained by using three or more perpendicular lines does not necessarily converge to one point.

    In such a case, a plurality of intersection positions determined by the above procedure are calculated, and an average value of the plurality of intersection positions is set as the center position of the Lissajous waveform 4. If the center position is obtained by performing the intersection averaging process, the influence of the error of the center position can be reduced.

FIG. 5 is a diagram showing the relationship between the center position of the Lissajous waveform and the origin position. When the Lissajous waveform is an ideal waveform, the center position of the Lissajous waveform is assumed to be the origin (0, 0). Further, the coordinates of the center position of the Lissajous waveform obtained by the above procedure are assumed to be (x ₀ , y ₀ ). At this time, when the amplitude (signal strength) of the output signal 1a is taken on the horizontal axis and the amplitude (signal strength) of the output signal 1b is taken on the vertical axis, it is expressed as shown in FIG.

When the center position of the Lissajous waveform is obtained as shown in FIG. 5 from the actually measured Lissajous waveform, the amplitude-time characteristics of the output signals 1a and 1b are shown in FIG. In FIG. 6, the offset of the output signal 1a is 9a, and the offset of the output signal 1b is 9b. By subtracting x ₀ and y ₀ corresponding to the coordinates of the center position from the output signals 1a and 1b, the coordinates of the center position of the Lissajous waveform can be corrected to the origin (0, 0).

    FIG. 7 shows the waveform of the output signal after offset correction. Offset components are removed from the corrected output signals 1a 'and 1b'. By the correction by the above procedure, it is possible to obtain output signals 1a 'and 1b' having no offset as shown in FIG.

  Next, offset correction of the output signal in the present embodiment will be described in detail with reference to a flowchart. FIG. 10 is a flowchart showing the procedure for obtaining the offset correction value.

  First, the position detection apparatus 100 detects a two-phase output signal that is output when the object to be measured moves slightly (S101), and takes in the correction signal 50 into the two-phase output signal (S102). The captured two-phase output signal is represented as an X coordinate and a Y coordinate on the Lissajous waveform, as in the position (x, y).

The correcting unit 50 determines whether or not the number of executions of capturing the output signal has reached a preset number N (S103). Here, the number of times N is set to 3 or more (N ≧ 3). If the number of executions has not reached the number N, 1 is added to the number N and Steps S101 and S102 are repeated. These steps are executed until the number of executions reaches the number N. When the number of executions reaches the number N, the position (coordinates) (x, y) ((x ₁ , y ₁ ) (x ₂ , y ₂ )... (X _N , _N ) on the Lissajous waveform y _N )) is obtained.

    In this way, in steps S101 to S103, at least three points on the Lissajous waveform are captured from the two-phase output signal. That is, at least the amplitude of the first two-phase output signal, the amplitude of the second two-phase output signal, and the amplitude of the third two-phase output signal are captured.

When a plurality of positions (x, y) on the Lissajous waveform are obtained, next, two of these positions are selected, and the positions of the two points are set so as to pass through the midpoint of these two positions. A perpendicular line is drawn (S104). For example, the perpendicular line is drawn on the basis of two points of the position (x _N , y _N ) and the position (x _N−1 , y _N−1 ), which are positions for adjacent N. However, the method for selecting two points out of a plurality of positions is not limited to the above method, and other methods may be used.

  In step S104, at least a step of obtaining two perpendicular lines, a first perpendicular line and a second perpendicular line, is executed. The first perpendicular passes through the midpoint of the first position obtained from the amplitude of the first two-phase output signal and the second position obtained from the amplitude of the second two-phase output signal, and the first position It is a line perpendicular to a straight line connecting the second position. The second vertical line passes through the midpoint of the second position obtained from the amplitude of the second two-phase output signal and the third position obtained from the amplitude of the third two-phase output signal. It is a line perpendicular to the straight line connecting the position and the third position.

When a plurality of perpendicular lines are drawn in step S104, the intersection (x ₀ , y ₀ ) of the two perpendicular lines is obtained based on the two perpendicular lines (S105). That is, the intersection of the first perpendicular line and the second perpendicular line is obtained.

It should be noted that at least one intersection (x ₀ , y ₀ ) of two perpendiculars may be obtained. However, in order to improve accuracy, a plurality of intersection points can be obtained. In this case, the number of points on the Lissajous waveform captured in step S102 is increased, and as many vertical lines as necessary are drawn in step S104. In step S105, k (k ≧ 2) intersections (x _0k , y _0k ) are calculated for a plurality of perpendicular pairs.

When a plurality of intersections (x _0k , y _0k ) are obtained, it is determined whether or not the values of the plurality of intersections match (S106). Here, the phrase “a plurality of intersections match” means that the positions of the intersections completely match on the digital signal. However, it may be determined that the intersection points match when the positions of the intersection points do not completely match but substantially match. The substantial coincidence range can be appropriately set in consideration of the detection accuracy of the position detection device and the like.

In step S106, if the values of a plurality of intersection points (x _0k , y _0k ) match, this value is the center position of the Lissajous waveform. The offset of the output signal is the difference between the center position of the Lissajous waveform and the origin (0, 0). Therefore, the value for moving the center position to the origin becomes the offset correction value, and the procedure for obtaining the offset correction value is completed. Also, in the case of a configuration in which only one intersection is obtained, the procedure for obtaining the offset correction value ends at this point.

  If the values of the plurality of intersections do not match, the plurality of intersections are averaged to obtain an average value of the intersections (S107). The average value of the plurality of intersections can be easily obtained by dividing the sum of the values of the plurality of intersections by the number of intersections. The average value of the obtained intersection points is set as the center position of the Lissajous waveform. The offset of the output signal is the difference between the center position of the Lissajous waveform and the origin (0, 0). Therefore, the value for moving the center position to the origin is the offset correction value, and the procedure for obtaining the offset correction value is completed.

  When the correction is completed by the procedure shown in FIG. 10, the position detection device 100 operates to detect the position of the object to be measured using the offset correction value. At this time, the position detecting device 100 corrects the offset of the two-phase output signal by subtracting the difference (offset correction value) between the intersection position and the origin position from the two-phase output signal, and thereby the position of the object to be measured. Is detected.

    The position of the object to be measured is obtained by calculating the arc tangent of the amplitude ratio of the two-phase output signal after offset correction. At this time, it is desirable to prepare in advance a table showing the relationship between the output signal amplitude ratio and the arc tangent calculation result. When the amplitude ratio of the output signal is calculated, the position of the object to be measured can be detected with a simple process by referring to a table created in advance.

  As described above, according to the present embodiment, it is possible to provide a highly accurate position detection device and position detection method. In particular, according to the present embodiment, the center position of the Lissajous waveform is obtained from at least three points of the Lissajous waveform of the output signal, and the offset based on the difference between the center position and the origin position is corrected, thereby providing a highly accurate offset. It can be corrected.

  The offset correction is performed by subtracting the difference between the center position and the origin position from the output signal so that the center position becomes the ideal origin position.

    In particular, a fine positioning is required in applications in which offset fluctuation due to location is a problem. That is, it is used for positioning several points per rotation of the Lissajous waveform, like a servo track write of a hard disk. In such a case, positioning is performed on one Lissajous waveform or a nearby Lissajous waveform. Therefore, an offset near a certain period can be obtained by calculating using three or more points on the Lissajous waveform.

    Normally, the offset does not fluctuate rapidly. For this reason, in an application in which stepped positioning is repeated, such as servo track writing, the offset of the area to be used next can be regarded as being substantially equal to the offset of the current position. Such stepped positioning is performed in a normal use state. For this reason, no special operation is required for offset correction. Even when the operating region gradually changes, the offset correction amount is automatically adjusted.

  As described above, the present invention has been specifically described based on examples. However, the present invention is not limited to the matters described in the above embodiments, and can be appropriately modified without departing from the technical idea of the present invention. The application target of the present invention is not limited to the encoder, and can be applied to other apparatuses such as a laser interferometer for measuring the stage position of the exposure apparatus.

It is the schematic of the position detection apparatus in a present Example. (A) The amplitude-time characteristic of the output signal. (B) Lissajous waveform of the output signal. It is a figure which shows the relationship between the position on a Lissajous waveform, and a center position. It is a figure which shows how to obtain | require the perpendicular which passes along the midpoint of a 1st position and a 2nd position. It is a figure which shows the relationship between a center position and an origin position. It is a figure which shows the offset of an output signal. It is a figure which shows the output signal after offset correction | amendment. It is the figure which showed an example of the structure of the servo track writer in a hard disk drive. It is a figure which shows the relationship between an offset and the error of a divided signal. It is a flowchart which shows the procedure which calculates | requires the correction value of the offset in a present Example.

Explanation of symbols

1a, 1b: output signals 2a, 2b: analog-digital conversion means 3: digital operation means 4: Lissajous waveform 5: first straight line 7: second straight line 6: first perpendicular 8: second perpendicular 9a: output Signal 1a offset 9b: Output signal 1b offset 10: Media 11: Swing arm 12: Magnetic head 13: Push pin 14: Positioning mechanism 15: Servo track signal 50: Correction means 51: Offset calculation means 52a, 52b: Subtraction means 100: Position detection device

Claims (4)

A position detection device that detects the position of the object to be measured based on a two-phase output signal that is output in accordance with a change in the position of the object to be measured,
Analog-to-digital conversion means for digitally converting the two-phase output signal and outputting a digital signal;
Correction means for correcting the offset of the digital signal by calculating the center position of the Lissajous waveform using at least three points on the Lissajous waveform generated by the digital signal;
And a digital calculation means for calculating the position of the object to be measured using the signal corrected by the correction means. The correction means includes
Offset calculating means for calculating the center position of the Lissajous waveform using three points at the first position, the second position, and the third position on the Lissajous waveform;
Subtracting means for subtracting the difference between the center position and the origin position calculated by the offset calculating means from the digital signal output from the analog-digital converting means,
The offset calculating means includes
A first perpendicular line passing through a midpoint of a first straight line connecting the first position and the second position on the Lissajous waveform and perpendicular to the first straight line;
A second perpendicular line passing through a midpoint of a second straight line connecting the second position and the third position on the Lissajous waveform and perpendicular to the second straight line;
The position detection apparatus according to claim 1, wherein an intersection position between the first perpendicular line and the second perpendicular line is calculated as the center position.     3. The position detection apparatus according to claim 2, wherein the offset calculation unit calculates a plurality of intersection positions and sets an average value of the plurality of intersection positions as the center position. A position detection method for detecting the position of the object to be measured based on a two-phase output signal output in accordance with a change in the position of the object to be measured,
Capturing the amplitude of the first two-phase output signal, the amplitude of the second two-phase output signal, and the amplitude of the third two-phase output signal from the two-phase output signal;
On the Lissajous waveform of the two-phase output signal, the first position obtained from the amplitude of the first two-phase output signal and the midpoint of the second position obtained from the amplitude of the second two-phase output signal And determining a first perpendicular perpendicular to a first straight line passing through the first position and the second position;
On the Lissajous waveform of the two-phase output signal, the second position obtained from the amplitude of the second two-phase output signal and the third position obtained from the amplitude of the third two-phase output signal Obtaining a second perpendicular line passing through a point and perpendicular to a second straight line connecting the second position and the third position;
Determining an intersection position between the first perpendicular and the second perpendicular;
Correcting the offset of the two-phase output signal by subtracting the difference between the intersection position and the origin position from the two-phase output signal;
Detecting the position of the object to be measured using a correction value obtained by correcting the offset.