DESCRIPTION
Title of Invention: ANGULAR ERROR CORRECTION DEVICE AND ANGULAR ERROR CORRECTION METHOD FOR POSITION SENSOR
Technical Field
[0001] The present invention relates to an angular error correction device and an angular error correction method for a position sensor for correcting an angular error in a position sensor including a periodic error uniquely determined in accordance with the rotational position of an electric motor, the position sensor being used in, for instance, control devices of elevator traction machines, control devices of automotive electric motors, and control devices of electric motors in machine tools.
Background Art
[0002] Conventional angle detection devices are known wherein: an angle signal is detected from a signal detected by an angle detector in a resolver ; a position error is calculated by an angular error estimator by referring to the detected angle signal by relying on a feature whereby an error waveform of the resolver is formed from an n-th order component determined specifically for the resolver, and by exploiting the reproducibility of the error waveform; a speed error signal is calculated by differentiating the position error; a detection error for each frequency component is calculated through frequency analysis of the speed error signal, for instance on the basis of a Fourier transform; an estimated angular error signal is generated by combining the calculated detection errors; and the detected angle signal is corrected by an angle signal correction circuit, using the generated estimated angular error signal (see for instance PTL 1 ).
Citation List Patent Literature

[0003] [PTL 1] Japanese Patent Application Publication No. 2012-145371
Summary of Invention
Technical Problem
[0004] The following problems arise however in conventional art.
In speed detection using a conventional resolver device or angle detection device of a resolver, angular error is estimated by detecting the rotational speed of a motor through differentiation of an angle signal detected by an angle detector, and by subjecting then the detected speed to Fourier transform analysis. When estimating an angular error using detected speed, the estimation precision of the angular error is determined by the positional resolution of the angle detection device and by the sampling time (time resolution) in speed calculation. This is problematic in that, as a result, a quantization error arises in angle detection devices of low positional resolution, and sufficient estimation precision of angular error fails to be achieved.
[0005] Methods for estimating angular error according to a method different from those of conventional examples are problematic in that, even in cases where angular error of good estimation precision is obtained beyond the resolution of a position sensor, the resolution of the position sensor constitutes a bottleneck when correcting an angle signal detected by a position sensor using the obtained angular error, and thus a sufficient correction effect fails to be achieved.
[0006] It is an object of the present invention, arrived at in order to solve the above problems, to provide an angular error correction device and angular error correction method for a position sensor that allow estimating angular error accurately and that allow sufficiently correcting the angular error.
Solution to Problem

[0007] The angular error correction device for a position sensor according to the present invention is an angular error correction device for a position sensor that detects a rotational position of an electric motor and corrects an angular error of the position sensor including a periodic error uniquely determined in accordance with the rotational position, this device including: an angular error estimator which estimates the angular error for the rotational position of the electric motor detected by the position sensor; and an angular error correction unit which corrects the angular error by using an angular error estimated value which is an output of the angular error estimator, wherein the angular error correction unit corrects the angular error, by using the angular error estimated value, after having multiplied by a (a is an integer of 2 or more) the rotational position of the electric motor detected by the position sensor.
[0008] Also, the angular error correction device for a position sensor according to the present invention is an angular error correction device for a position sensor that detects a rotational position of an electric motor and corrects an angular error of a position sensor including a periodic error uniquely determined in accordance with the rotational position, this device including: an angular error estimator which estimates the angular error for the rotational position of the electric motor detected by the position sensor; and an angular error correction unit which corrects the angular error by using an angular error estimated value which is an output of the angular error estimator, wherein the angular error correction unit utilizes a value resulting from multiplying the angular error estimated value by 1/y (y is a positive number) to correct the angular error for the rotational position of the electric motor detected by the position sensor.
Advantageous Effects of Invention
[0009] In the angular error correction device for a position sensor according to the present invention, the position sensor detects a rotational position of an electric motor including a periodic error uniquely determined in accordance with

the rotational position. The angular error estimator estimates the angular error for the rotational position of the electric motor detected by the position sensor, and the angular error correction unit corrects the angular error by using an angular error estimated value which is an output of the angular error estimator.
The angular error correction unit multiplies the rotational position of the electric motor detected by the position sensor by a (a is an integer of 2 or more), and thereafter corrects an angular error by using an angular error estimated value, or corrects the angular error for the rotational position of the electric motor detected by the position sensor by using a value resulting from multiplying the angular error estimated value by 1/y (y is a positive number).
Accordingly, it becomes possible to make the angular error corrected value for correction higher than the resolution of the position sensor, and hence there can be achieved an angular error correction device and angular error correction method for a position sensor that allow estimating angular error accurately and that allow sufficiently correcting the angular error.
Brief Description of Drawings
[0010] Fig. 1 is a block diagram illustrating the overall configuration of a control device of an electric motor having an angular error correction device for a position sensor according to the present invention.
Fig. 2 is a block diagram illustrating a control device of an electric motor in which there is used an angular error correction device for a position sensor according to Embodiment 1 of the present invention.
Fig. 3 is a block diagram illustrating a control device of an electric motor in which there is used an angular error correction device for a position sensor according to Embodiment 1 of the present invention.
Fig. 4 is a graph illustrating an example of detection error in a position sensor of the angular error correction device for a position sensor according to Embodiment 1 of the present invention.

Fig. 5 is a block diagram illustrating an angular error estimation unit of the angular error correction device for a position sensor according to Embodiment 1 of the present invention.
Fig. 6 is a block diagram illustrating a detected position correction unit of the angular error correction device for a position sensor according to Embodiment 1 of the present invention, depicted together with an angular error estimator and a position sensor.
Fig. 7 is an explanatory diagram illustrating the effect of an angular error correction device for a position sensor according to Embodiment 1 of the present invention.
Fig. 8 is a block diagram illustrating a detected position correction unit of the angular error correction device for a position sensor according to Embodiment 2 of the present invention, depicted together with an angular error estimator and a position sensor.
Description of Embodiments
[0011] Preferred embodiments of the angular error correction device and angular error correction method for a position sensor according to the present invention will be explained next with reference to accompanying drawings. In the explanation that follows, identical or corresponding portions in the figures will be denoted with identical reference symbols.
[0012] In the embodiments below a method will be explained that allows sufficiently correcting an angular error, regardless of the resolution of a position sensor, in an angular error correction device for a position sensor that estimates and then corrects, on the basis of the current flowing in the electric motor, a position-dependent angular error included in the rotational position of an electric motor, which is the output of a position sensor.
In the embodiments below, examples will be explained of an estimation method that involves estimating an angular error on the basis of current, but so

long as the estimation method does not depend on the resolution of the position sensor, the method can also be used in other estimation methods. [0013] Embodiment 1
Fig. 1 is a block diagram illustrating the overall configuration of a control device of an electric motor having an angular error correction device for a position sensor according to the present invention. Figs. 2 and 3 are block diagrams illustrating control devices of an electric motor in which there is used the angular error correction device for a position sensor according to Embodiment 1 of the present invention.
[0014] In Figs. 1 to 3, the control device of an electric motor is provided with a speed command value generation unit 1, a speed controller 2, a current controller 3, an inverter 4, an electric motor 5, a position sensor 6, a current sensor (current detection unit) 7, a speed computing unit 8, a detected position correction unit (angular error correction unit) 9, a position computing unit 11, a coordinate converter 12 and an angular error estimation unit 20. [0015] The speed command value generation unit 1 generates and outputs a speed command value for the electric motor 5. Although not illustrated in the figures, the speed command value generation unit 1 may include a position control system. The present invention can also be used in a case where the speed command value generation unit 1 includes a position control system. [0016] The speed controller 2 has, as the input thereof, a difference between the speed command value from the speed command value generation unit 1 and the rotational speed of the electric motor 5, as calculated by the speed computing unit 8; herein, the speed controller 2 generates and outputs a current command value for the electric motor 5.
[0017] The speed computing unit 8 calculates, and then outputs, the rotational speed of the electric motor 5 on the basis of position information resulting from correction, by the detected position correction unit 9, of the rotational position of the electric motor 5 being the output of the position sensor 6. Most simply, the

speed computing unit 8 calculates the rotational speed through time differentiation of the position.
[0018] The speed computing unit 8 may calculate the speed on the basis of position information (for instance number of pulses in an optical encoder) from the position sensor 6. The speed computing unit 8 may include a configuration for measuring time.
4
[0019] The current controller 3 has, as the input thereof, a difference between the current command value from the speed controller 2 and a phase current being the output of the current sensor 7 illustrated in Fig. 2, or an axial current of the electric motor 5 resulting from conversion of the phase current illustrated in Fig. 3 to for instance d-q axes, by the coordinate converter 12. The current controller 3 generates and outputs a voltage command value of the electric motor 5.
[0020] The position computing unit 11 calculates, and outputs, angle information of the electric motor 5 on the basis of the position information corrected by the detected position correction unit 9. In the case of vector control of the electric motor 5, the coordinate converter 12 converts the phase current from the current sensor 7 to coordinates suitable for control, for instance a-(3 axes, d-q axes or y-5 axes.
[0021] The detected position correction unit 9 adds/subtracts an angular error estimated value which is the output of the angular error estimation unit 20, to/from the rotational position of the electric motor 5 being the output of the position sensor 6, and outputs the corrected position information. The detailed function of the detected position correction unit 9 will be described below. [0022] The current sensor 7 measures the current in the electric motor 5. In a case where, for instance, the electric motor 5 is a three-phase electric motor, there are often measured phase currents of two phases, but also phase currents of three phases may be measured herein. In Figs. 1 to 3, the current sensor 7 measures output current of the inverter 4, but alternatively, the current sensor 7

may estimate respective phase currents through measurement of a bus current of the inverter 4, as in a current measurement scheme by a one-shunt resistor. This does not affect the present invention in any way.
[0023] The inverter 4 converts the voltage of a power source, not shown, to desired variable voltage and variable frequency, on the basis of the voltage command value from the current controller 3. In the present invention, the inverter 4 denotes a variable-voltage variable-frequency power converter such as a power converter in which AC voltage is converted to DC voltage by a converter, and the DC voltage is thereafter converted to AC voltage by an inverter, for instance as in inverter devices that are available in the market, or alternatively, a power converter that converts AC voltage directly to AC variable voltage and variable frequency, as in matrix converters. [0024] The inverter 4 according to Embodiment 1 of the present invention may include the function of coordinate conversion, in addition to the function of the inverter 4 described above. In a case where the voltage command value is a voltage command value in the d-q axes, specifically, the term inverter 4 encompasses instances where the latter has also a coordinate conversion function of conversion to voltage according to an instructed voltage command value, through conversion of the voltage command value in the d-q axes to phase voltage or to line voltage. The present invention can also be used when there is provided a device or means, not shown, for correcting the dead time of the inverter 4.
[0025] The position sensor 6, for instance an optical encoder, magnetic encoder, resolver or the like, detects the rotational position of the electric motor 5, as required to control the latter. As illustrated in Fig. 4, the rotational position information outputted by the position sensor 6 includes a periodic error uniquely determined in accordance with the rotational position of the electric motor 5. [0026] Herein, the periodic error that is uniquely determined in accordance with the rotational position of the electric motor 5 denotes for instance a detection

error of the resolver described in PTL 1 (paragraphs [0020] and [0021), as well as errors having reproducibility in accordance with the rotational position, such as missing pulses or inter-pulse distance imbalance derived from slit defects in an optical encoder.
[0027] The periodic error uniquely determined in accordance with the rotational position of the electric motor 5 will be expressed hereafter as an angular error 9err resulting from conversion of position information to an angle. The present invention can be used in a case where the position sensor 6 includes a periodic error uniquely determined in accordance with the rotational position of the electric motor 5, and a main component order of the angular error 9err is known. [0028] The periodic angular error 9eiT of the position sensor 6 can be approximated by a sine wave, as given in Expression (1) below. In Embodiment 1 of the present invention the notation has been unified in the form of a sine wave, since there is no substantial difference in notation by sine waves or cosine waves. [0029] [Math. 1]
0errxA]sm(N]em+(pi) + A2sm(N20m+(p2) + --- + Ansm(Nnem+(pn) • • • (1)
[0030] In Expression (1), 9m denotes the mechanical angle of the electric motor 5, Ai denotes an error amplitude of Nrth order, A2 denotes an error amplitude of N2-th order, An denotes an error amplitude of Nn-th order, cp, denotes a phase shift (error phase) of Nrth order with respect to the mechanical angle of the electric motor 5, (p2 denotes a phase shift of N2-th order with respect to the mechanical angle of the electric motor 5, and (pn denotes a phase shift of Nn-th order with respect to the mechanical angle of the electric motor 5. [0031] The spatial orders N,, N2...Nn in Expression (1), which need not be consecutive integers such as 1, 2...Nn, are the spatial orders of the main component of the periodic error uniquely determined in accordance with the

rotational position of the electric motor 5. Herein the term main component denotes a component the spatial order amplitude of which is larger than the amplitude at other frequencies.
[0032] Three or more frequency components are combined in the notation of Expression (1), but the frequency component of the periodic angular error 9err may be formed from one, two or more components.
[0033] Fig. 5 is a block diagram illustrating an angular error estimation unit of the angular error correction device for a position sensor according to Embodiment 1 of the present invention. In Fig. 5, the angular error estimation unit 20 has a frequency analysis unit 21 and an angular error estimator 22. [0034] The frequency analysis unit 21 has, as inputs thereof, the phase current from the current sensor 7, and the angle information of the electric motor 5 resulting from correction, by the detected position correction unit 9, of the rotational position of the electric motor 5 being the output of the position sensor 6, and being calculated by the position computing unit 11; herein the frequency analysis unit 21 obtains an amplitude, or amplitude and phase, at a desired frequency of the input current.
[0035] Preferably, the frequency analysis unit 21 has a configuration wherein , there is obtained the amplitude and phase at a desired frequency of the signal that is inputted, for instance as in a Fourier transform, a Fourier series analysis or a fast Fourier transform. However, the frequency analysis unit 21 may be configured to extract a desired frequency signal, as in a filter that combines a notch filter and a band pass filter, and to calculate the desired amplitude and phase of the input signal, by way of an amplitude detection unit and a phase detection unit. The filter that is used herein may be an electrical filter, being a combination of resistors, capacitors, coils and the like, or may be a process executed in a computer.
[0036] In Embodiment 1 of the present invention, in particular, the frequency analysis unit 21 may have any configuration as long as the feature thereof allows

detecting information proportional to the amplitude at the desired frequency or information proportional to the power of the amplitude. In Fig. 2 phase current is the input, but there may be inputted any one of a d-axis current and a q-axis current, a y-axis current and a 5-axis current, or an a-axis current and a (3-axis current, resulting from coordinate conversion of the phase current, as illustrated in Fig. 3.
[0037] The term signal at a desired frequency (specific frequency) denotes herein a signal of frequency identical to that of the main component of angular error 9err5 derived from the periodic angular error 0eiT of the position sensor 6. In Embodiment 1 of the present invention the desired frequency is expressed as spatial frequency, but no essential difference would arise by using temporal frequency.
[0038] The term spatial frequency denotes frequency in a specific interval, which in Embodiment 1 of the present invention is one rotation of the electric motor 5. Further, a signal of N periodic waves per machine rotation of the electric motor 5 is referred to as a wave of spatial order N. [0039] In the control device of the electric motor 5 that is provided with the position sensor 6, the error of the position sensor 6 has periodicity in accordance with the rotational position of the electric motor 5. Therefore, frequency analysis involves preferably analysis by spatial frequency. In Expression (1) as well, the angular error 0err is expressed on the basis of spatial frequency. The inputs of the frequency analysis unit 21 illustrated in Figs. 1 to 3 are inputs (current and angle) corresponding to spatial frequency analysis. [0040] However, Embodiment 1 of the present invention can be used also in frequency analysis by temporal frequency. In the case of frequency analysis by temporal frequency, frequency analysis is carried out using, as inputs, a detected speed, a measured time by a time measurement unit, and current, instead of using current and angle as inputs.

[0041] The angular error estimator 22 has, as inputs, the current amplitude value of the desired frequency component, which is the output of the frequency analysis unit 21, and the angle information of the electric motor 5 resulting from correction, by the detected position correction unit 9, of the rotational position of the electric motor 5 being the output of the position sensor 6, and being calculated by the position computing unit 11. The angular error estimator 22 estimates, in accordance with the estimation method described below, the periodic angular error Qerr that is uniquely determined in accordance with the rotational position of the electric motor 5, and outputs the angular error estimated value.
[0042] One of the inputs of the detected position correction unit 9 is the output signal (rotational position of the electric motor 5) of the position sensor 6, and hence the angular error estimator 22 outputs the position information. In a conceivable specific instance where the position sensor 6 is an optical encoder having a resolution of 1024 pulses/rotation, and the estimation result of the angular error estimator 22 is 1 °, then the angular error estimator 22 outputs, as the position information, three pulses corresponding to 1°. [0043] In a case where the frequency component of the angular error is a plurality of components, as denoted by Expression (1), it suffices to estimate successively the angular errors of respective components, and to summate the errors, or to estimate simultaneously the plurality of frequency components. The estimation time can be shortened in simultaneous estimation as compared with that in successive estimation of the angular errors of respective components. For the sake of simplicity, an instance is explained herein where the angular error is formed only from a single frequency component.
[0044] It is found that when speed feedback control is performed by the position sensor 6 that includes the periodic angular error uniquely determined in accordance with the rotational position of the electric motor 5, there occurs a pulsation of the current command value or current pulsation including a

frequency component of the same order as that of the angular error. Accordingly, the angular error and the error in the rotational position of the electric motor 5 as calculated using the output of the position sensor 6 can be reduced by estimating and correcting the angular error so as to suppress such current pulsation.
[0045] In a case where the position sensor 6 includes a periodic error uniquely determined in accordance with the rotational position of the electric motor 5, the current pulsation that appears in the phase current upon execution of frequency analysis of the phase current by the frequency analysis unit 21, when the electric motor 5 is a permanent magnet synchronous motor, is of (Pn ± N„)-th order in terms of mechanical order, where Pn denotes the number of pole pairs and Nn denotes the order of the desired frequency.
[0046] Accordingly, it is sufficient to perform frequency analysis of at least one-phase current, from among the various phase currents, and to estimate a (Pn + Nn)-th or (Pn - Nn)-th order angular error on the basis of a (Pn + Nn)-th or (Pn -Nn)-th order current. However, there is a possibility that the (Pn - Nn)-th order takes on a negative value, and is thus non-existent, in a case where the order Nn of the desired frequency is larger than the number of pole pairs Pn of the electric motor 5. It is therefore preferable to perform frequency analysis of the (Pn + Nn)-th order current. Constant-torque and constant-speed operation is preferred when estimating the angular error.
[0047] Upon analysis of the frequency of either one of the d-axis current and the q-axis current, by the frequency analysis unit 21, the current pulsation components appearing in the d-q axes have a component that pulsates at the same order as that of the Nn-th order, on account of the angular error of mechanical Nn-th order. The d-axis current exhibits current pulsation analogous to that of angular error, since the q-axis current, being a torque current, revolves on account of magnetic pole offset derived from the angular error. The speed pulsation of the q-axis current constitutes a pulsation of the current command

value, through a speed control system. Accordingly, the q-axis current constitutes a current pulsation analogous to the angular error giving rise to the speed pulsation.
[0048] Therefore, the angular error estimator 22 may for instance estimate the angular error so as to minimize the N„-th order current amplitude of the d-axis current or of the q-axis current, obtained through frequency analysis in the frequency analysis unit 21.
[0049] In frequency analysis using any one of the current command values or any one of the current detected values of the d-axis current or the q-axis current, estimation is performed under a condition whereby the revolving q-axis current is fixed, i.e. a condition of constant acceleration. In particular, estimation is preferably performed under a condition whereby acceleration is zero, i.e. the electric motor 5 is rotating at constant speed.
[0050] The detailed function of the detected position correction unit 9 will be described next. Firstly, to estimate and correct a position-dependent angular error included in the rotational position of the electric motor 5, which is the output of the position sensor 6, the angular error estimated value outputted by the angular error estimation unit 20 was converted to position information of the position sensor 6, and the result was fitted to the detected value of the position sensor 6.
[0051] In a case where, for instance, the position sensor 6 is an optical encoder that expresses output position information in the form of an AB phase, correction was carried out by using a result of discretizing the angular error estimated value in accordance with the resolution D of the optical encoder, in a count of AB phase pulses of the optical encoder.
[0052] Accordingly, the resolution D' of the angular error estimator was conventionally identical to the resolution D of the position sensor 6. The angle per pulse of the position sensor 6 and the angular error estimator is given by Expression (2).

[0053] 360/D = 360/D' (7 pulse) ■ ■ • (2)
[0054] In Embodiment 1 of the present invention, however, the angular error
estimation unit 20 estimates the angular error estimated value on the basis of the
current flowing in the electric motor 5, and hence the resolution D' of the
angular error estimator 22 is determined by the resolution of the current sensor 7,
and there are cases where the resolution D' of the angular error estimator is
higher than the resolution D of the position sensor 6 (D' > D).
[0055] In such cases the resolution D of the position sensor 6 becomes a
bottleneck when correcting the angular error of the position sensor 6 using the
angular error estimated value from the angular error estimator 22. The angular
error can only be corrected at the resolution D of the position sensor 6 being
smaller than the original resolution D' of the angular error estimator 22, and thus
a sufficient correction effect fails to be achieved.
[0056] In a conceivable specific instance, there holds resolution D' = 3600
(360/D' = 0.1 (7 pulse)) for the angular error estimator 22, and resolution
D=720 (360/D = 0.5 (7 pulse)) for the position sensor 6.
[0057] In this case, the angular error estimator 22 can estimate the angular error
estimated value in 0.1° increments, but when correcting the correction of the
angular error of the position sensor 6, position information (pulses) is corrected
in 0.5° increments, due to the influence of the resolution D of the position sensor
6.
[0058] Therefore, to correct the angular error of the position sensor 6 using the
angular error estimated value from the angular error estimation unit 20 a method
will be explained in Embodiment 1 of the present invention that allows
achieving a sufficient correction effect by multiplying the resolution D of the
position sensor 6 by a (a is an integer of 2 or more), as a result of which the
resolution of the detected position correction unit 9 is brought to aD, which is
higher than the resolution D of the position sensor 6.

[0059] Fig. 6 is a block diagram illustrating a detected position correction unit of the angular error correction device for a position sensor according to Embodiment 1 of the present invention, depicted together with an angular error estimator and a position sensor. In Fig. 6, the detected position correction unit 9 has a high-resolution position conversion unit 91, a discretization processing unit 92, a multiplier 93, a position corrector 94 and a 1/multiplier 95. [0060] The high-resolution position conversion unit 91 discretizes the angular error estimated value from the angular error estimator 22 at a resolution aD. The discretization processing unit 92 discretizes the position information of the position sensor 6 at a resolution D. The multiplier 93 multiplies the output of the discretization processing unit 92 by a. The position corrector 94 uses the angular error estimated value resulting from discretization by the high-resolution position conversion unit 91 in the output of the multiplier 93, and outputs the position information after correction. The 1/multiplier 95 multiplies the output of the position corrector 94 by 1/a.
[0061] Thus the result from discretizing the detected value of the position sensor 6 is multiplied by a, is corrected by the angular error estimated value, and the corrected result is multiplied by 1/a. In consequence, the resolution of the detected position correction unit 9 can be artificially increased up to a-fold aD, from the resolution D position sensor 6. The upper limit of the resolution aD of the detected position correction unit 9 is the resolution D' of the angular error estimator 22.
[0062] In the above example, specifically, the resolution of the detected position correction unit 9 can be set to, at most, a resolution D' = 3600 of the angular error estimator 22, from a resolution D = 720 of the position sensor 6. Thus the detected position correction unit 9 can correct the angular error of the position sensor 6 at a five-fold resolution.

[0063] With 9eiT herein as the angular error estimated value, a discrete value Pe in a case where the angular error estimated value Qerr is discretized at the resolution D of the position sensor 6 is given by Expression (3) below. [0064] Pe « eerr*D/27r • • • (3)
[0065] A discrete value Pe' in a case where the angular error estimated value 9etT* is discretized at resolution aD obeys the relationship given by Expression (4) below.
Pe' * 0err*aD/27r = aPe + p • • • (4) [0066] In Expression (4), P is a discrete value newly appearing as a result of a high-resolution discretization process, with the P being herein an integer such that p < a.
[0067] Defining Ps as a discrete value resulting from discretizing the position information of the position sensor 6 at resolution D, the number of pulses after conventional correction is Ps - Pe, whereas the number of pulses after correction in Embodiment 1 of the present invention is [0069] In Embodiment 1 of the present invention, the angular error of the position sensor 6 can be corrected at a precision now higher by p/a, according to Expression (5). Fig. 7 illustrates the effect of the angular error correction device for a position sensor according to Embodiment 1 of the present invention. In Fig. 7, A denotes the angular error estimated value, B denotes pulses after conventional correction, and C denotes pulses after correction according to Embodiment 1 of the present invention.
[0070] In Embodiment 1 above, thus, the position sensor detects a rotational position of an electric motor including a periodic error uniquely determined in accordance with the rotational position; the current detection unit detects the current flowing in the electric motor; the frequency analysis uses the rotational

position of the electric motor to analyze the frequency of the current detected by the current detection unit, and calculates an amplitude of a specific frequency component corresponding to the angular error; the angular error estimator estimates, as an angular error estimated value, the angular error formed from the specific frequency component on the basis of the amplitude calculated by the frequency analysis unit and the rotational position of the electric motor; the angular error correction unit utilizes the angular error estimated value to correct the angular error for the rotational position of the electric motor detected by the position sensor.
Herein, the angular error correction unit corrects the angular error, using the angular error estimated value, after having multiplied by a (a is an integer of 2 or more) the rotational position of the electric motor detected by the position sensor.
Accordingly, the angular error can be estimated accurately, and can be corrected sufficiently. [0071] Embodiment 2
A method has been explained in Embodiment 1 above in which, when correcting the angular error of the position sensor 6 using the angular error estimated value from the angular error estimation unit 20, the resolution D of the position sensor 6 is multiplied by a (a is an integer of 2 or more), as a result of which the resolution of the detected position correction unit 9 is brought to aD, which is higher than the resolution D of the position sensor 6, and thus a sufficient correction effect can be obtained thereby.
[0072] In Embodiment 2, by contrast, a method will be explained which, when correcting the angular error of the position sensor 6 using the angular error estimated value from the angular error estimation unit 20, through multiplication, by 1/y (y is a positive number), of the angular error estimated value resulting from discretization at a resolution yD, to correct thereby the angular error of the position sensor 6 by a decimal or fractional pulse higher than the resolution D of

the position sensor 6 and thus a sufficient correction effect can be obtained thereby.
[0073] Fig. 8 is a block diagram illustrating a detected position correction unit of the angular error correction device for a position sensor according to Embodiment 2 of the present invention, depicted together with an angular error estimator and a position sensor. In Fig. 8, the detected position correction unit 9 has a high-resolution position conversion unit 91, a discretization processing unit 92, a 1/multiplier 95 and a position corrector 94.
[0074] The high-resolution position conversion unit 91 discretizes the angular error estimated value from the angular error estimator 22 at a resolution yD. The discretization processing unit 92 discretizes the position information of the position sensor 6 at a resolution D. The 1/multiplier 95 multiplies the output of the position corrector 94 by 1/y. The position corrector 94 uses the angular error estimated value resulting from discretization by the high-resolution position conversion unit 91 and having been multiplied by 1/y in the 1/multiplier 95, in the output of the discretization processing unit 92, and outputs the position information after correction.
[0075] Thus, the value resulting from discretizing at a resolution yD the angular error estimated value from the angular error estimator 22 is multiplied by 1/y, and the obtained value is used correct the angular error of the position sensor 6 by a decimal or fractional pulse higher than the resolution D of the position sensor 6.
[0076] Taking the resolution D of the position sensor 6 as a reference, it becomes accordingly possible to correct the angular error by a 1/y fractional pulse, and to artificially increase the resolution of the detected position correction unit 9 from the resolution D of the position sensor 6 up to y-fold yD. Herein, y denotes the ratio of the resolution D' of the angular error estimator 22 and the resolution D of the position sensor 6.

[0077] In Embodiment 2 above, thus, the position sensor detects a rotational position of an electric motor including a periodic error uniquely determined in accordance with the rotational position, the current detection unit detects the current flowing in the electric motor, the frequency analysis uses the rotational position of the electric motor to analyze the frequency of the current detected by the current detection unit, and calculates an amplitude of a specific frequency component corresponding to the angular error; the angular error estimator estimates, as an angular error estimated value, the angular error formed from the specific frequency component on the basis of the amplitude calculated by the frequency analysis unit and the rotational position of the electric motor; the angular error correction unit utilizes the angular error estimated value to correct the angular error for the rotational position of the electric motor detected by the position sensor.
The angular error correction unit utilizes a value resulting from multiplying the angular error estimated value by 1/y (y is a positive number) to correct the angular error for the rotational position of the electric motor detected by the position sensor.
Accordingly, the angular error can be estimated accurately, and can be corrected sufficiently.
[0078] In Embodiment 2 above an instance has been explained in which the angular error of the position sensor 6 is corrected using a fractional pulse, but the present invention can be likewise used, and the same effect can be achieved, when correcting the angular error of the position sensor 6 using a decimal pulse. [0079] Correction in the constant multiple method of Embodiments 1 and 2 may involve, for instance in an example of an optical encoder, processing mathematically a position information signal denoted by the pulses after discretization, or performing bit shifting by means of a shifter.

CLAIMS
[Claim 1] An angular error correction device for a position sensor that
detects a rotational position of an electric motor and corrects an angular error of the position sensor including a periodic error uniquely determined in accordance with the rotational position, the device comprising:
an angular error estimator which estimates the angular error for the rotational position of the electric motor detected by the position sensor; and
an angular error correction unit which corrects the angular error by using an angular error estimated value which is an output of the angular error estimator,
wherein the angular error correction unit corrects the angular error by using the angular error estimated value, after having multiplied by a (a is an integer of 2 or more) the rotational position of the electric motor detected by the position sensor.
[Claim 2] An angular error correction device for a position sensor that detects a rotational position of an electric motor and corrects an angular error of the position sensor including a periodic error uniquely determined in accordance with the rotational position,
the device comprising:
an angular error estimator which estimates the angular error for the rotational position of the electric motor detected by the position sensor; and
an angular error correction unit which corrects the angular error by using an angular error estimated value which is an output of the angular error estimator,
wherein the angular error correction unit utilizes a value resulting from multiplying the angular error estimated value by 1/y (y is a positive number) to

correct the angular error for the rotational position of the electric motor detected by the position sensor.
[Claim 3] The angular error correction device for a position sensor of claim 1 or 2, further comprising:
a current detection unit which detects current flowing in the electric motor; and
a frequency analysis unit which, by using the rotational position of the electric motor, analyzes the frequency of the current detected by the current detection unit and calculates an amplitude of a specific frequency component corresponding to the angular error,
wherein the angular error estimator estimates, as an angular error estimated value, the angular error formed from the specific frequency component on the basis of the amplitude calculated by the frequency analysis unit and the rotational position of the electric motor.
[Claim 4] A method for correcting an angular error of a position sensor, the method being executed by an angular error correction device for the position sensor that detects a rotational position of an electric motor and corrects an angular error of the position sensor including a periodic error uniquely determined in accordance with the rotational position, and the method comprising:
an angular error estimation step of estimating the angular error, as an angular error estimated value; and
an angular error correction step of correcting by using the angular error estimated value the angular error for the rotational position of the electric motor detected by the position sensor,
wherein the angular error correction step comprises:

a step of multiplying by a (a is an integer of 2 or more) the rotational position of the electric motor detected by the position sensor; and
a step of correcting the angular error, by using the angular error estimated value, for the rotational position of the electric motor having been multiplied by a.
[Claim 5] A method for correcting an angular error of a position sensor, the method being executed by an angular error correction device for the position sensor that detects a rotational position of an electric motor and corrects an angular error of the position sensor including a periodic error uniquely determined in accordance with the rotational position, and the method comprising:
an angular error estimation step of estimating the angular error, as an angular error estimated value; and
an angular error correction step of correcting by using the angular error estimated value the angular error for the rotational position of the electric motor detected by the position sensor,
wherein the angular error correction step comprises:
a step of multiplying the angular error estimated value by 1/y (y is a positive number); and
a step of correcting the angular error by using the angular error estimated value, which has been multiplied by 1/y, for the rotational position of the electric motor detected by the position sensor.
[Claim 6] The angular error correction method for a position sensor of
claim 4 or 5, further comprising:
a current detection step of detecting current flowing in the electric motor;
a frequency analysis step of analyzing by using the rotational position of the electric motor the frequency of the current detected in the current detection

step and calculating an amplitude of a specific frequency component corresponding to the angular error,
wherein in the angle estimation step of estimating, as an angular error estimated value, the angular error formed from the specific frequency component on the basis of the amplitude calculated in the frequency analysis step and the rotational position of the electric motor.