JP2007171081A - Position detection method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a position detection method capable of performing accurate position detection by using one A/D converter. <P>SOLUTION: An estimated value corresponding to data before one sampling period of one signal is calculated from sampling data before two sampling periods of one signal and sampling data before one sampling period of the other of data MRA'(n), MRB'(n) acquired by sampling alternately at a prescribed sampling period a sine wave signal output from two MR (Magnetoresistive) elements for position detection, and the amplitude of the sine wave signal is calculated from the estimated value and sampling data before one sampling period of the other signal. The amplitude and sampling data of this time of one signal are applied to an inverse trigonometric function, to thereby determine the object position. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a position detection method using an output signal of a magnetoresistive element (hereinafter referred to as “MR element”) applied to focusing of an optical lens.

  As a position detector for detecting the lens position of an optical system of a video camera, one having two MR elements arranged so as to be a sine wave signal whose output phase is shifted by 90 degrees is known. In this position detector, the sine wave signals respectively output from the two MR elements are converted from analog to digital, and arc tangent calculation is performed from the obtained pair of digital data, or data having better linearity at that position. The position of the lens is calculated by linear calculation using.

Here, when the outputs of the two MR elements are respectively sampled, the sampling timing shift is an error in the lens position, so the sampling timing is required to be the same time. Therefore, a two-channel analog-to-digital converter (hereinafter referred to as “A / D converter”) is used for this processing, or a pair of one-channel A / D converters is used as disclosed in Patent Document 1. A configuration combining the sample and hold circuit and the multiplexer is required.
Japanese Patent No. 3173531

  In recent years, a microcomputer (microcomputer) is often used for a control circuit. Many microcomputers switch multi-channel analog inputs to a single A / D converter by switching, and perform digital data conversion. In this case as well, there is a problem in sampling timing deviation due to switching depending on the control target. Also, the calculation time may be a problem when the detection position error due to the sampling timing deviation is corrected by calculation with the preceding data. On the other hand, in the case of a microcomputer equipped with a plurality of A / D converters operating in parallel (or arranged externally), the occurrence of errors due to variations in device characteristics, cost, power consumption, etc. are problems. .

  The present invention has been made paying attention to this point, and an object thereof is to provide a position detection method capable of performing accurate position detection using one A / D converter.

  In order to achieve the above object, the invention described in claim 1 is applied to a position detection system of an optical system of an imaging apparatus in which a plurality of magnetoresistive elements are arranged so as to output a sine wave signal and a cosine wave signal. In the position detection method for determining the position of the object based on the sine wave signal and the cosine wave signal output from the magnetoresistive element, the sine wave signal and the cosine wave signal are alternately sampled at a predetermined sampling period. Corresponds to data of one signal before one sampling period from sampling data before one sampling period of one of the sine wave signal and cosine wave signal and sampling data before one sampling period of the other signal. Whether an estimated value is calculated, and the calculated estimated value and the sampling data of the other signal one sampling period before Calculating the amplitude of the sine wave signal and the cosine wave signal, and applying the calculated amplitude and the current sampling data of the one signal to a corresponding inverse trigonometric function to determine the position of the object. A position detection method is provided.

  According to the first aspect of the present invention, outputs from a plurality of magnetoresistive elements arranged so as to output a sine wave signal and a cosine wave signal are alternately sampled at a predetermined sampling period, and two samplings of one signal are performed. An estimated value corresponding to the data before one sampling period of one signal is calculated from the sampling data before the period and the sampling data before the other one sampling period. The amplitude of the sine wave and cosine wave is calculated from this estimated value and the sampling data of the other signal one sampling period before, and this amplitude and the current sampling data of one signal are applied to the corresponding inverse trigonometric function. A position is required. Thereby, the exact position of a target object can be detected using one A / D converter.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a block diagram showing a configuration of a video camera drive device to which a position detection method according to an embodiment of the present invention is applied. This apparatus includes an optical system 1 including a lens 10. The optical system 1 includes a linear motor 3 that drives the lens 10 and a position detection unit 2 that includes two MR elements for detecting the position of the lens 10. And. From the position detection unit 2, output signals SA and SB of the two MR elements are output, amplified by the amplifiers 4 and 5 and supplied to the control unit 6 and the comparators 15 and 16, respectively. The comparators 15 and 16 determine the sign (positive / negative) of the signals output from the amplifiers 4 and 5, respectively, and supply a signal indicating the determination result to the CPU 14.

  The control unit 6 includes a multiplexer 11, a sample and hold circuit 12, an A / D converter 13, and a CPU (Central Processing Unit) 14. The signals SA and SB are alternately selected by the multiplexer 11 and input to the sample and hold circuit 12. The A / D converter 13 converts the output signal level of the sample and hold circuit 12 into digital values (hereinafter referred to as “MR element output values”) MRA and MRB, and inputs them to the CPU 14. The CPU 14 controls the position of the lens 10 by driving the linear motor 3 via the drive circuit 7 while detecting the lens position of the optical system 1 using the MR element output values MRA and MRB. The CPU 14 further controls the multiplexer 11, the sample hold circuit 12, and the A / D converter 13. The CPU 14 also adjusts the DC offset voltage of each of the amplifiers 4 and 5 via the 2-channel D / A converter 17.

  FIG. 2 is a waveform diagram showing an example of the signals SA and SB output from the two MR elements when the lens 10 is driven at a constant speed v. The MR elements are arranged so that the signals SA and SB become sine wave signals whose phases are shifted by 90 degrees, that is, sine wave signals and cosine wave signals. The signals SA and SB are signals in which a sine wave signal is superimposed on a DC offset voltage.

式（１）、（２）、（３）において、Ａは振幅値、λは図２の波形１周期に対応する距離（波長）、Ｘはレンズ１０の位置座標、ｘは周期内のレンズの相対位置座標、Ｐ及びＱはオフセット値、ｍは「０」以上の整数である。 Here, it is assumed that signal levels, that is, MR element output values MRA and MRB are expressed by the following equations (1) and (2), respectively.

In equations (1), (2), and (3), A is the amplitude value, λ is the distance (wavelength) corresponding to one period of the waveform in FIG. 2, X is the position coordinate of the lens 10, and x is the lens in the period. Relative position coordinates, P and Q are offset values, and m is an integer greater than or equal to “0”.

  When the video camera is activated or reset, the DC offset voltage of the MR element is measured, and then the drive coil of the linear motor 3 moves to the end and stops, and the respective output values MRA0 and MRB0 is actually measured. The actually measured output values MRA 0 and MRB 0 are converted into digital values by the A / D converter 13 and input to the CPU 14.

In the following description, a method for detecting a position based on outputs MRA ′ and MRB ′ obtained by correcting DC offset voltages P and Q represented by the following formulas (1a) and (2a) will be described. The DC offset voltages P and Q are adjusted by the CPU 14 to the midpoint voltage level of the A / D converter 13.

  FIG. 3 shows waveforms of the outputs MRA 'and MRB' calculated by the equations (1a) and (2a). The actually measured output values MRA0 and MRB0 at the end are shown as MRA'0 and MRB'0 in FIG. Since the actual end coordinates do not necessarily match X = 0, ΔX is calculated from MRA'0, and the position coordinates are corrected.

Conventionally, using the MRA ′ and MRB ′ measured at the same time, the relative position coordinate x of the lens within the period is calculated by the following equation (4).

However, because of the above-described problems, MRA ′ and MRB ′ are measured alternately instead of simultaneously in this embodiment, and arc sine calculation is performed on MRA ′ as shown in the following equations (5) and (6). For MRB ′, arc cosine calculation is applied to calculate the relative position coordinate x of the lens within the period.

Here, since the amplitude value A varies depending on the position of the linear motor 3, the value calculated based on the sampled MRA 'and MRB' is used for the amplitude value A without using a previously measured value. Now, MR element output value MRA [n] (n is the discretization time indicating the sampling time) is subjected to A / D conversion and offset correction MRA ′ [n], and amplitude value A [n calculated one sample before -1] is used to express x [n], the following equation (7) is obtained.

In calculating the amplitude value A [n−1], the unsampled MRA ′ [n−1] is estimated by the following equation (8). However, it is assumed that the lens moves at a constant speed and the sampling phase interval θ is constant.

Since MRA ′ [n−2] in Expression (8) is sampled, a method for calculating MRB ′ [n−2] that has not been sampled will be described below. Since the sampled MRB ′ [n−1] is given by the following formula (9), MRB ′ [n−2] is given by the following formula (10).

式（１１）の右辺のＭＲＡ’［ｎ−２］、ＭＲＢ’［ｎ−１］はサンプリングされた実測値であり、また等位相間隔θの値は等速変位の速度とサンプリング時刻の間隔から得られるので、推定値ＭＲＡ’［ｎ−１］を算出することができる。 When the relationship of Expression (10) is applied to Expression (8), the following Expression (11) is obtained.

MRA ′ [n−2] and MRB ′ [n−1] on the right side of the equation (11) are sampled actual measured values, and the value of the equiphase interval θ is calculated from the velocity of the constant velocity displacement and the interval of the sampling time. Since it is obtained, the estimated value MRA ′ [n−1] can be calculated.

式（１３）により求められた振幅値Ａ［ｎ−１］と実測値であるＭＲＡ’［ｎ］を式（７）に適用し、周期内の相対位置座標ｘ［ｎ］が求められる。 Here, the estimated value MRA ′ [n−1] and the actually measured value MRB ′ [n−1] obtained and the amplitude value A [n−1] have the relationship of the following formula (12). The amplitude value A [n−1] is obtained from the equation (13).

The amplitude value A [n−1] obtained by the equation (13) and the actually measured value MRA ′ [n] are applied to the equation (7), and the relative position coordinate x [n] within the period is obtained.

  For MRB ', the required amplitude value can be obtained from the two actually measured values by the same method as that for obtaining the amplitude value A [n-1], and the relative position coordinates in the cycle can be obtained.

  Next, which of the two inverse trigonometric functions existing in one cycle is selected is determined by the combination of the signs of MRA 'and MRB'. The signs of MRA 'and MRB' are determined by reading the outputs of the comparators 15 and 16 with the CPU. Now, assuming that the calculation result of the inverse trigonometric function is φ and the relative position coordinate in the period to be obtained is x, when MRA ′ ≧ 0 and MRB ′ ≧ 0, both the arcsine calculation result and the arccosine calculation result are x = λφ. / 2π. When MRA ′ ≧ 0 and MRB ′ <0, the arc sine calculation result is x = λ (π−φ) / 2π, and the arc cosine calculation result is x = λφ / 2π. When MRA '<0 and MRB' <0, the arc sine calculation result is x = λφ / 2π, and the arc cosine calculation result is x = λ (2π−φ) / 2π. When MRA ′ <0 and MRB ′ ≧ 0, the arc sine calculation result is x = λ (3π−φ) / 2π, and the arc cosine calculation result is x = λ (2π−φ) / 2π.

  As described above, in the present embodiment, the sine wave signals output from the two MR elements are alternately A / D converted (sampled) at a predetermined sampling period, and the position coordinates are calculated by an inverse trigonometric function. There is no need to consider the sampling timing shift, and accurate position detection can be performed using one A / D converter.

  Next, another detection method for increasing the accuracy of the calculated position coordinates will be described. Taking a sine wave as an example, the rate of change is small near 90 degrees and 270 degrees, and the accuracy of the inverse trigonometric function calculation decreases. Therefore, in this method, MRA ′ is sampled in the sections corresponding to the phase angles of 0 ° to 45 °, 135 ° to 225 °, and 315 ° to 360 °, and the phase angles correspond to 45 ° to 135 °, 225 ° to 315 °. In the interval, MRB ′ is sampled. Specifically, MRA 'is sampled in a section where | MRA' | ≤ | MRB '|, and MRB' is sampled in a section where | MRA '|> | MRB' |.

When this method is employed, it may be necessary to obtain MRA ′ [n−2] from the actually measured value of MRB ′ [n−2] in the equation (8). In this case, if the equation (9) is modified, the following equation (14) is obtained. Therefore, MRA ′ [n−2] is calculated from the two actually measured values MRB ′ [n−2] and MRB ′ [n−1]. Can be calculated.

  By this method, the position coordinates can be calculated without using the sampling data of the section corresponding to the phase angle at which the accuracy of the inverse trigonometric function calculation is lowered, and the accuracy of the calculated position coordinates can be improved.

It is a block diagram which shows the structure of the lens drive device of the video camera to which the position detection method concerning one Embodiment of this invention is applied. It is a wave form diagram of the signal output from MR element. It is a waveform diagram of the MR element output signal after correcting the DC offset component.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Optical system 2 MR element unit 3 Linear motor 6 Control unit 10 Lens 14 CPU

Claims (1)

A sine wave signal and a cosine output from the magnetoresistive element are applied to a position detection system of an optical system of an imaging apparatus, in which a plurality of magnetoresistive elements are arranged to output a sine wave signal and a cosine wave signal. In a position detection method for determining the position of an object based on a wave signal,
The sine wave signal and the cosine wave signal are alternately sampled at a predetermined sampling period,
One of the sine wave signal and the cosine wave signal corresponds to data of one signal before one sampling period from sampling data of two signals before one sampling period and sampling data of one signal before one sampling period. Calculate an estimate,
Calculating the amplitudes of the sine wave signal and the cosine wave signal from the calculated estimated value and the sampling data of the other signal one sampling period before;
A position detection method characterized in that the position of the object is obtained by applying the calculated amplitude and the current sampling data of the one signal to a corresponding inverse trigonometric function.

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