JP2008148484A - Positioning device of shaft type linear motor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a positioning device of a shaft type linear motor, which can be employed in a field requiring compaction by reducing the setting range of a magnetic scale by limiting the detection region and enables positioning device of a moving segment even in a region where the magnetic scale is not set, while the positioning device performs highly accurate positioning with a linear scale. <P>SOLUTION: The positioning device of the shaft type linear motor includes a first position detecting means 4A which performs position detection in a detection region partially set in the linear driving range of the moving segment 3 and a second position detecting means 4B which performs position detection over the entire linear driving range. The first position detecting means 4A is constituted of a linear scale capable of performing precise position detection, while the second position detecting means 4B detects the position of the moving segment 3 by detecting the magnetic flux of a shaft 2 with a magnetic sensor S provided on the moving segment 3. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a positioning device for a shaft type linear motor that linearly drives a mover along a shaft.

  In recent years, shaft-type linear motors have attracted attention as electric actuators that are linearly driven. This type of shaft-type linear motor includes a shaft in which a plurality of bar-shaped magnets are arranged in series, and a mover that is slidably fitted to the shaft, and a coil provided on the inner periphery of the mover. The mover is driven linearly by excitation. According to such a configuration, since there is little cogging and speed unevenness, application in various fields is being studied.

When positioning control of a shaft type linear motor is performed, a position detecting unit for detecting the position of the mover is usually added separately (for example, see Patent Documents 1 to 3). As this type of position detection means, a linear scale (linear encoder) is generally used, and precise positioning is possible. However, the linear scale is composed of a magnetic head (position information reading unit) provided on the mover and a magnetic scale (position information storage unit) arranged opposite to each other along the movement trajectory of the magnetic head. Since the position of the mover is detected by reading the magnetic scale of the magnetic scale, the magnetic scale must be arranged in parallel over the entire length of the shaft. As a result, there is a problem that the periphery of the shaft type linear motor is enlarged, and the use in a field where compactness is required is limited.
JP 2004-125699 A JP 2004-129440 A JP 2004-129441 A

  The present invention was devised to eliminate the above-described problems, and performs high-accuracy positioning using a linear scale, while limiting the detection section to reduce the installation range of the magnetic scale. Thus, a shaft type linear motor positioning device capable of detecting the position of the mover even in a section where a magnetic scale is not installed can be used even in a field where downsizing is required. It is intended to provide.

  In order to solve the above-mentioned problems, a positioning apparatus for a shaft type linear motor according to the present invention includes a shaft in which a plurality of bar-shaped magnets are arranged in series, and a mover that is slidably fitted on the shaft. A shaft type linear motor positioning device that linearly drives the movable element by excitation of a coil provided on an inner peripheral portion of the element, and in a detection section partially set in a linear driving range of the movable element First position detection means for detecting the position of the mover, and second position detection means for detecting the position of the mover in the linear drive range excluding the detection section of the first position detection means, or in the entire linear drive range. The first position detecting means includes a position information reading unit provided in the mover, and a position information storage unit arranged in an opposing manner along a movement trajectory of the position information reading unit, The position information reading unit performs position detection of the mover by reading position information in the position information storage unit, and the second position detection unit includes a magnetic sensor provided in the mover, and the magnetic sensor The position of the mover is detected by detecting the magnetic flux of the shaft.

  Although the present invention is configured as described above to perform highly accurate positioning using a linear scale, it is required to be compact by limiting the detection section and reducing the installation range of the magnetic scale. In addition, the position of the mover can be detected even in a section where the magnetic scale is not installed.

  DESCRIPTION OF THE PREFERRED EMBODIMENTS A shaft type linear motor positioning device that exemplifies an embodiment of the present invention as a preferred embodiment will be described below in detail with reference to the drawings. FIG. 1 is a perspective view of a shaft type linear motor (magnetic scale is omitted) according to an embodiment of the present invention. As shown in this figure, the shaft type linear motor 1 includes a shaft 2 in which a plurality of rod-shaped magnets 2a are arranged in series, and a mover 3 that is slidably fitted to the shaft 2 and includes the mover. The mover 3 is linearly driven by excitation of a coil (not shown) provided on the inner peripheral portion of the arm 3.

  When positioning control of such a shaft type linear motor 1 is performed, position detecting means 4 for detecting the position of the mover 3 is added. The positioning device for the shaft type linear motor 1 according to the present invention includes a first position detecting means 4A for detecting the position of the mover 3 in a detection section partially set in the linear drive range of the mover 3, and a first position. It is characterized in that it includes a linear drive range excluding the detection section of the detection means 4A, or a second position detection means 4B that detects the position of the mover 3 in the entire linear drive range, and hereinafter, the first position detection means 4A and The second position detection unit 4B will be described.

  The second position detection means 4B is configured to include a magnetic sensor (Hall element or the like) S provided on the mover 3, and detects the position of the mover 3 based on a change in magnetic flux of the shaft 2 detected by the magnetic sensor S. Do. That is, according to the second position detecting means 4B, the position of the mover 3 is detected using the magnetic flux change of the shaft 2 without providing a magnetic scale like a linear scale. The linear motor 1 can be made compact.

  As a position detection method of the mover 3 by the magnetic sensor S, first, a method of obtaining a position (mechanical angle) by calculation from two-phase analog signals output from the two magnetic sensors S can be considered. This method is based on the premise that the analog signals obtained from the two magnetic sensors S are sine waves orthogonal to each other. That is, when the magnetic flux distribution of the shaft 2 is not sinusoidal, an error occurs in the obtained position information. In the actual shaft 2, it is difficult to say that the magnetic flux distribution is sinusoidal and includes many spatial harmonics. Thus, it is conceivable to remove the spatial harmonics by smoothing the magnetic flux penetrating the magnetic sensor S by moving the magnetic sensor S away from the shaft 2, but it is difficult to completely remove the harmonics. Moreover, since the output level of the magnetic sensor S decreases, there is a concern about the deterioration of the SN ratio and the influence of disturbance due to external magnetic flux.

  FIG. 2 is a block diagram showing a detection concept of the second position detection means applied to the shaft type linear motor positioning device according to the embodiment of the present invention. As shown in this figure, the position detection method of the second position detection means 4B according to the embodiment of the present invention is a plurality of (for example, four) magnets arranged at predetermined intervals in the axial direction of the shaft 2. Two-phase analog signals are obtained by using the sensors S0 to S3 and multiplying the outputs of the magnetic sensors S0 to S3 by respective predetermined weighting factors. The number of magnetic sensors S needs to be appropriately selected according to the filtering characteristics to be obtained, but at least two are necessary. In practical use, although there are problems to be solved such as an increase in cost due to the use of many magnetic sensors S and variations in detection sensitivity of the magnetic sensors S, there is an advantage that the filtering characteristics can be easily determined by selecting the number. If a waveform close to a sine wave can be extracted from the magnet portion of the shaft, an analog signal output from a magnetic sensor (for example, S0 to S3) can be directly used for position detection.

  When the weighting factor calculation and the addition calculation are performed by the operational amplifier circuit, two-phase analog signals (A-phase and B-phase orthogonal signals) can be obtained with a very simple circuit configuration. In this case, since the obtained two-phase signal may be input to the controller, the controller may have two A / D inputs as in the conventional case, and the existing controller can be used as it is. On the other hand, when the weighting factor calculation and the addition calculation are performed inside the controller microcomputer, A / D inputs are required for the number of the magnetic sensors S. However, variations in sensitivity of the magnetic sensors S can be absorbed by software processing. There is an advantage. It is also possible to change the weight coefficient inside the microcomputer as required.

  FIG. 3 is a graph showing an example of the magnetic flux density distribution of the shaft. As shown in this figure, the magnetic flux density distribution in the vicinity of the surface of the shaft 2 includes many spatial harmonics instead of a sine wave. Here, consider a configuration in which seven magnetic sensors S are used and arranged at intervals of 5 mm. The weighting factors to be multiplied by the magnetic sensors S0 to S6 are set as shown in FIG. When the interval between the magnetic sensors S0 to S6 is 5 mm and the period of the magnetic flux distribution is 60 mm, if the sampling is performed at 12 times the period of the magnetic flux, it is set to pass about 1.44 harmonics or less of the magnetic flux period. It can be said. The two-phase signal obtained using this coefficient setting is shown in FIG. As shown in this figure, it can be seen that the harmonics are greatly reduced and are almost sinusoidal. FIG. 6 shows a position error obtained by calculation from the two-phase signal.

  FIG. 8 shows an analog two-phase output when six magnetic sensors S0 to S5 are arranged at intervals of 5 mm and a band-pass filter is configured so as to extract only the third harmonic component contained in the magnetic flux distribution of the shaft 2. It is. The weighting factor was set as shown in FIG. Here, since the third harmonic is used, if a resolution of 0.1 mm is required, the calculation requires a resolution of 1.8 deg. However, the accuracy is higher than the method using the fundamental wave. Becomes easier. FIG. 9 shows an error when position detection is performed by calculation. When a higher resolution is targeted, fine adjustment such as correction is required.

  The spatial harmonics on the surface of the shaft 2 have a considerably large fifth harmonic, and if the magnetic sensor S is brought as close to the shaft 2 as possible, position detection using the fifth harmonic is sufficiently possible. In this case, the number of magnetic sensors S is large, but stable and high accuracy can be obtained. FIG. 11 shows the result of detecting the fifth harmonic using ten magnetic sensors S at intervals of 3 mm. The weighting factor was set as shown in FIG. Here, since the interval between the magnetic sensors S is narrow, it is expected that it will be difficult to arrange the magnetic sensors S in a line. However, if the surface-mounted chip type magnetic sensor having a small size is arranged, the magnetic sensors S are arranged in a line. Can do.

  Further, as shown in FIGS. 12A to 12C, the magnetic sensors S may be arranged in a plurality of rows. For example, as shown in FIG. 12A, five magnetic sensors S may be arranged so as to face each other by 180 ° with the shaft 2 interposed therebetween. In this case, the magnetic sensors S in each row are arranged at an interval of 6 mm so that the substantial interval is 3 mm. Even with such an arrangement, a fifth-order harmonic two-phase signal that can be used for position detection can be obtained. Further, by arranging each row of the magnetic sensors S symmetrically (facing the front) or by shifting the positions thereof, for example, compared to a case where ten magnetic sensors S are arranged in a row, the mover 3 The length can be shortened to ½, which is effective for downsizing. In addition, when each row is disposed so as to be displaced, sensoring can be performed with respect to the value of the phase difference of the magnetic flux, and detection accuracy and detection efficiency can be improved.

  Next, positioning control by the second position detecting means 4B will be described with reference to FIG. FIG. 13 is a block diagram showing a shaft type linear motor positioning control system (second position detecting means) according to an embodiment of the present invention. As shown in this figure, the positioning control system for positioning the shaft type linear motor 1 by the second position detecting means 4B includes a plurality of magnetic sensors S, a mixing unit 5, an A / D conversion unit 6, a digital signal processing unit 7, A D / A conversion unit 8, a current amplifier unit 9 and the like can be provided.

  In the present embodiment, ten magnetic sensors S0 to S9 are arranged at intervals of 3 mm. For example, Hall elements are used as the magnetic sensors S0 to S9. The output of each Hall element is detected by a differential amplifier. The ten analog signals obtained in this way are mixed by the mixing unit 5.

  As described above, the mixing unit 5 obtains a two-phase analog signal by multiplying the outputs of the magnetic sensors S0 to S9 by respective predetermined weighting factors and adding them. For example, the mixing unit 5 of the present embodiment is composed of 24 OP amplifiers, but it can be realized with 8 to 12 OP amplifiers.

  The A / D converter 6 is an A / D converter for taking in the fifth-order harmonic two-phase signal (5A, 5B) and the fundamental two-phase signal (1A, 1B) into the digital signal processing unit 7. 6a.

  The digital signal processing unit 7 is, for example, a DSP (Digital Signal Processor), and includes a position estimating unit 11, an estimated position correcting unit 12, a motor driving unit 13, and the like. The position estimation unit 11 calculates the phase angle θ from the fifth-order harmonic two-phase signal (5A, 5B) captured by the A / D converter by the calculation block 11a. Since fifth-order harmonics are detected, θ changes by 2π when moved by 1/5 of the actual magnetic flux period of 60 mm, that is, 12 mm. This θ is monitored by the circulation counter block 11b, and the number N of rotations of the phase angle θ is counted. Then, the estimated position is calculated by the estimated position acquisition block 11c using the phase angle θ and the number of rotations N.

  The estimated position correction unit 12 corrects the estimated position calculated by the position estimation unit 11. That is, since the estimated position obtained by the position estimating unit 11 includes an error due to variations in magnet length and magnetic flux density, the estimated position is corrected using the correction data. The correction data is created in advance by the correction data table block 12a. For example, the difference between the linear scale value and the estimated position is recorded at an interval of 0.1 mm. The correction data table block 12a is at the estimated position. The corresponding error value is given. For example, the error value of the estimated position 5.23 mm is obtained by reading the error values of 5.2 mm and 5.3 mm from the table and linearly interpolating the two points to obtain an approximate value. Then, the corrected estimated position is obtained by subtracting the correction data from the estimated position, and the corrected estimated position is input to the motor drive unit 13 to execute PID control.

  The motor drive unit 13 generates a coil current command from the fundamental two-phase signals (1A, 1B). The phase shift block 13a adjusts the phase of the two-phase signal (1A, 1B) so that the torque angle becomes appropriate. After adjusting the phase, only the 1B phase is shifted by 30 ° to obtain a two-phase signal having a phase difference of 120 °. By multiplying the two-phase signal by the output value of the PID block 13b, a coil current value is obtained that provides a propulsive force proportional to the PID output. The current amplifier unit 9 is configured using a power OP amplifier 9a. That is, the power supply to the shaft type linear motor 1 is not the PWM system, but the power OP amplifier 9a is used to supply a current proportional to the command signal. Of course, a PWM current amplifier can also be used. The command signal for the current amplifier unit 9 is performed via the D / A conversion unit 8 including the D / A converter 8a.

  Next, the detection accuracy of the second position detection unit 4B according to the embodiment of the present invention will be described with reference to FIGS. FIG. 14 shows a position detection error when correction by the correction data table is not performed. As shown in this figure, when correction by the correction data table is not performed, an error of about ± 0.6 mm is generated. However, in applications that do not require high accuracy, it can be used without correction.

  FIG. 15 shows the position detection error after correction by the correction data table in which the difference between the linear scale value and the estimated position is recorded at intervals of 0.5 mm. FIG. 16 shows the difference between the linear scale value and the estimated position at intervals of 0.2 mm. FIG. 17 shows the position detection error after correction by the correction data table in which the difference between the linear scale value and the estimated position is recorded at intervals of 0.1 mm. . As shown in these figures, the error after correction by the correction data table is reduced according to the correction data interval, but considering the increase in the number of correction data, in the example of this embodiment, the 0.2 mm interval is balanced. The correction data is preferable.

  Next, the first position detection unit 4A will be described with reference to FIG. FIG. 18 is an explanatory diagram showing the configuration of the first position detecting means applied to the shaft type linear motor positioning device according to the embodiment of the present invention. As shown in this figure, the first position detection means 4A includes a magnetic head T as a position information reading unit provided in the movable element 3, and a position information storage arranged in an opposing manner along the movement locus of the magnetic head T. A magnetic linear scale (position detecting device) that detects the position of the mover 3 by reading the magnetic scale (position information) of the magnetic scale U with the magnetic head T. In addition, a laser type that combines a semiconductor laser as a light source and a photodetector at a light receiving portion with a hologram scale (hologram grating) as a diffraction grating, and basically uses the same operating principle as that of a rotary encoder. A photoelectric type that counts with a counter and measures the amount of displacement may be used. That is, the first position detection means 4A is a detection section partially set arbitrarily in the linear drive range of the mover 3 as described above (for example, A section and C section set as different detection stroke sections in FIG. , E section), the position of the mover 3 is detected only. That is, the position of the magnetic scale U can be reduced by performing position detection by the first position detection means 4A only in a section where high-precision positioning is required, so that the magnetic scale can be extended over the entire length of the shaft 2. Compared with the case where U is arranged in parallel, the periphery of the shaft type linear motor 1 can be made compact, and as a result, the use of the shaft type linear motor 1 can be promoted even in a field where compactness is required.

  In a section where the magnetic scale U is not installed (for example, section B and section D in FIG. 18), the position of the mover 3 can be detected by the second position detection means 4B. In the positioning operation (linear scale driving) by the first position detecting means 4A and the positioning operation (sensorless driving) by the second position detecting means 4B, the magnetic head T of the first position detecting means 4A reads the magnetic scale of the magnetic scale U. However, in order to switch the positioning operation (such as reset processing of the linear scale counter) reliably and quickly, the magnetic head T is provided with an origin sensor V, and the magnetic scale It is preferable to detect the origin position of U. The origin sensor V detects the origin detector W provided at the origin position of the magnetic scale U by a method different from that of the magnetic head T, and can be configured using, for example, a reflective optical sensor.

  Next, specific positioning control of the shaft type linear motor 1 using both the first position detecting means 4A (linear scale position detecting system) and the second position detecting means 4B (sensorless position detecting system) will be described with reference to FIGS. Will be described with reference to FIG. As shown in FIG. 19, the position information of the mover 3 by the first position detection means 4A and the second position detection means 4B is input to the driver X (or controller). The position information input from the first position detection means 4A to the driver X is precise position information in an arbitrary section, and also includes a detection signal from the origin sensor V. On the other hand, the position information input from the second position detection means 4B to the driver X is rough position information for all sections.

  The driver X internally processes the position information input from the first position detecting means 4A and the second position detecting means 4B by software, and drives the shaft type linear motor 1 to be positioned. Specifically, as shown in FIG. 20, first, it is determined whether or not the magnetic head T of the first position detecting means 4A detects the magnetic scale U (S1), and if this determination result is YES, Then, a positioning operation (linear scale driving) based on the position information of the first position detecting means 4A is performed (S2). Even in the linear scale driving state, the position detecting operation by the second position detecting means 4B is continued. On the other hand, if the determination result in step S1 is NO, a positioning operation (sensorless driving) based on the position information of the second position detecting means 4B is performed (S3). In this state, the origin detection by the origin sensor V is determined (S4). If the determination result is YES, the linear scale counter is reset (S5) and the process proceeds to linear scale drive (S2).

  In the embodiment of the present invention configured as described above, the positioning device for the shaft type linear motor 1 has first position detecting means 4A composed of a linear scale, and accurately detects the position of the mover 3. However, the position detection by the first position detection means 4A is performed only in the detection section partially set in the linear drive range of the mover 3 to one or a plurality of arbitrary strokes (may be different strokes). Therefore, the installation range of the magnetic scale U (position information storage unit) can be reduced. As a result, it is possible to make the periphery of the shaft type linear motor 1 more compact than in the case where the magnetic scale U is arranged along the entire length of the shaft 2, and as a result, the shaft type can be used even in fields where compactness is required. The use of the linear motor 1 can be promoted.

  In the section where the magnetic scale U is not installed, the position of the mover 3 can be detected by the second position detecting means 4B. That is, the second position detecting means 4B detects the position of the mover 3 by detecting the magnetic flux of the shaft 2, and can detect the position even in the section where the magnetic scale U is not installed.

  The positioning operation by the first position detection unit 4A and the positioning operation by the second position detection unit 4B are based on whether the magnetic head T of the first position detection unit 4A is reading the magnetic scale of the magnetic scale U. In this embodiment, since the origin sensor V is provided in the magnetic head T and the origin position of the magnetic scale U is detected, the positioning operation can be switched reliably and quickly. .

It is a perspective view of a shaft type linear motor (magnetic scale is omitted) according to an embodiment of the present invention. It is a block diagram which shows the detection concept of the 2nd position detection means applied to the positioning apparatus of the shaft type linear motor which concerns on embodiment of this invention. It is a graph which shows the magnetic flux density distribution example of a shaft. It is a table | surface figure which shows the weighting coefficient for a harmonic reduction. FIG. 5 is a waveform diagram of a two-phase analog signal obtained by the weighting factor of FIG. 4. It is explanatory drawing which shows the error of the estimated position calculated from the two-phase analog signal of FIG. It is a table | surface figure which shows the weighting coefficient for a 3rd harmonic extraction. FIG. 8 is a waveform diagram of a two-phase analog signal obtained by the weighting factor of FIG. 7. It is explanatory drawing which shows the error of the estimated position calculated from the two-phase analog signal of FIG. It is a table | surface figure which shows the weighting coefficient for 5th harmonic extraction. FIG. 11 is a waveform diagram of a two-phase analog signal obtained by the weighting factor of FIG. 10. (A)-(C) are perspective views which show the example of arrangement | positioning of a magnetic sensor. It is a block diagram which shows the positioning control system (2nd position detection means) of the shaft type linear motor which concerns on embodiment of this invention. It is explanatory drawing which shows the position detection error at the time of not correcting by a correction data table in the positioning control system of FIG. In the positioning control system of FIG. 13, it is explanatory drawing which shows the position detection error after the correction | amendment by the correction data table which recorded the difference of a linear scale value and an estimated position at 0.5 mm space | interval. In the positioning control system of FIG. 13, it is explanatory drawing which shows the position detection error after the correction | amendment by the correction data table which recorded the difference of a linear scale value and an estimated position by 0.2 mm space | interval. In the positioning control system of FIG. 13, it is explanatory drawing which shows the position detection error after the correction | amendment by the correction data table which recorded the difference of a linear scale value and an estimated position at 0.1 mm space | interval. It is explanatory drawing of a 2nd position detection means. It is a block diagram of the positioning control system which uses together a 1st position detection means and a 2nd position detection means. It is a flowchart of the positioning control system which uses together a 1st position detection means and a 2nd position detection means.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Shaft type linear motor 2 Shaft 2a Bar magnet 3 Movable element 4A 1st position detection means 4B 2nd position detection means 5 Mixing part 6 A / D conversion part 6a A / D converter 7 Digital signal processing part 8 D / A conversion Unit 8a D / A converter 9 current amplifier unit 9a power OP amplifier 11 position estimation unit 11a calculation block 11b circuit counter block 11c estimated position acquisition block 11d offset block 12 estimated position correction unit 12a correction data table block 13 motor drive unit 13a phase Shift block 13b PID block 14 Counter block S Magnetic sensor T Magnetic head U Magnetic scale V Origin sensor W Origin sensor X Driver

Claims (2)

A shaft having a plurality of rod-shaped magnets arranged in series and a mover that is slidably fitted to the shaft are provided, and the mover is linearly excited by excitation of a coil provided on the inner periphery of the mover. A shaft type linear motor positioning device to be driven by
First position detection means for detecting the position of the mover in a detection section partially set in the linear drive range of the mover;
A linear drive range excluding a detection section of the first position detection means, or a second position detection means for detecting the position of the mover in the entire linear drive range;
The first position detection unit includes a position information reading unit provided in the movable element, and a position information storage unit arranged in an opposing manner along a movement locus of the position information reading unit, and reads the position information. The position of the mover is detected by reading the position information in the position information storage unit at the unit,
The second position detection unit includes a magnetic sensor provided on the mover, and detects the position of the mover by detecting the magnetic flux of the shaft with the magnetic sensor. Positioning device.   2. The shaft type linear motor positioning apparatus according to claim 1, wherein the position information reading unit includes an origin sensor that detects an origin position of the position information storage unit.