JP2011061995A - Linear motor and position detecting method of linear motor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the following problem of a position detecting method of a linear motor: when a magnetic sensor is installed near a drive coil of the magnetic sensor, the accuracy in position detection is reduced owing to an influence of a magnetic field generated when power is supplied to the drive coil. <P>SOLUTION: The linear motor includes: a magnet in which a magnetic pattern for driving is magnetized along a linear drive direction, a drive coil which is arranged to face the magnet and generates a drive force in the drive direction against the magnet, and a plurality of magnetic sensors which are arranged to face each other on the side opposite to the drive coil against the magnet. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a linear motor and a linear motor position detection method.

  Conventionally, in a method for detecting the position of a linear motor, a method for detecting the position of a movable magnet by installing a magnetic sensor in a drive coil that is a stator and measuring a change in a magnetic field accompanying the movement of the movable magnet is known. (See Patent Document 1).

Japanese Patent Laid-Open No. 2000-92913

  However, when a magnetic sensor is installed in the vicinity of the drive coil, there is a problem in that the accuracy of position detection is reduced due to the influence of a magnetic field generated in response to energization of the drive coil.

  In order to solve the above-described problem, a linear motor according to a first aspect of the present invention includes a magnet in which a driving magnetic pattern is magnetized along a linear driving direction, and a magnet facing the magnet. And a plurality of magnetic sensors arranged opposite to the magnet on the opposite side of the drive coil.

  The above summary of the invention does not enumerate all necessary features of the present invention. In addition, a sub-combination of these feature groups can also be an invention.

It is a perspective view which shows typically the whole structure of a linear motor. It is sectional drawing which shows the structure of a linear motor schematically. It is a figure which shows the magnetic field distribution of the needle | mover in a Hall element position. It is a figure which shows the outline | summary of the magnetic field measurement result of a Hall element accompanying the movement of a needle | mover. It is a flowchart which shows the flow which detects the position of a needle | mover. It is the figure which showed the relationship between the output voltage of a Hall element, and the stroke position of a needle | mover.

  Hereinafter, the present invention will be described through embodiments of the invention, but the following embodiments do not limit the invention according to the claims. In addition, not all the combinations of features described in the embodiments are essential for the solving means of the invention.

  FIG. 1 is a perspective view schematically showing the overall structure of the linear motor 100 according to the present embodiment. The linear motor 100 includes a mover 110, a stator 120, a Hall element 130, a base member 140, a calculation unit 150, a guide rail 160, and a temperature sensor 170. The mover 110 is a cylindrical magnet, and its periphery is covered with a housing member. The stator 120 includes a central axis 122 and a drive coil 124 having a plurality of coils mounted around the central axis. The central shaft 122 is a ferromagnetic yoke and forms a magnetic circuit with the mover side magnet.

  The mover 110 is supported by the guide rail 160 and moves in the longitudinal direction of the guide rail 160. The stator 120 is supported by the support portion 142 of the base member 140. The stator 120 has an outer diameter smaller than the inner diameter of the mover 110. That is, the inner surface of the mover 110 is separated from the stator 120. Hereinafter, the moving direction of the mover 110 will be described as the X-axis direction, the direction orthogonal to the placement surface of the linear motor 100 as the Z-axis direction, and the direction orthogonal to the X-axis and the Z-axis as the Y-axis direction.

  The hall element 130 has a plurality of hall elements arranged on the base member along the X-axis direction. The plurality of Hall elements are arranged at positions facing the mover 110 and measure the magnetic field of the mover 110. In the present embodiment, 18 Hall elements are arranged at equal intervals.

  FIG. 2 is a sectional view schematically showing the structure of the linear motor 100. The mover 110 includes a magnet holder 112 and a magnet 114 fixed to the magnet holder 112. The magnet 114 is magnetized with a magnetic pattern in which magnetic poles are arranged in the X-axis direction as a driving magnetic pattern. This magnetic pattern has three sections, and a section having a width smaller than the center section width is magnetized at both ends of the center section. In this embodiment, the central partition width is twice the partition width at both ends.

  The drive coil 124 of the stator 120 has a plurality of coil groups each including three coils of U phase, V phase, and W phase, and each coil group is in the order of U phase, V phase, and W phase. They are arranged in the longitudinal direction of the stator 120. The width of each coil in the X-axis direction is the same, and is about 1/3 the width of the central section in the magnetic pole pattern of the magnet 114.

  The drive coil 124 is supplied with a three-phase current corresponding to a position having a phase difference of 120 degrees when the magnetic pole pitch (between NS) of the magnet 114 is 180 degrees, so that the magnetic force of the mover 110 is supplied. Thrust is generated in the X-axis direction due to the relationship with the pattern. Of the plurality of coils included in the drive coil 124, coils of the same phase are connected to the same current output terminal, and current is supplied through the current output terminal. By controlling the current supplied to the drive coil 124 in accordance with the position of the mover 110, the movement of the mover 110 in the X direction can be controlled.

  Here, if all the coils are energized, it is conceivable that the current supplied to the portions of the coils that do not contribute to the movement of the mover 110 is wasted and the efficiency is deteriorated. Therefore, in order to cope with this, a configuration may be adopted in which a switch is provided so that only a portion of the coil that contributes to the movement of the mover 110 is energized.

  The position of the mover 110 is detected using a plurality of hall elements 130 arranged. In order to measure the magnetic field of the magnet 114 of the mover 110 using the Hall element 130, the Hall element 130 is disposed at a position facing the mover 110. Here, it is conceivable to install the Hall element 130 in the drive coil 124. However, when the Hall element 130 is installed in the vicinity of the drive coil 124, it is easily affected by the magnetic field generated in response to the energization of the drive coil 124, and the position detection accuracy may be reduced.

  Therefore, in the present embodiment, the Hall element 130 is disposed on the opposite side of the drive coil 124 with respect to the magnet 114. With such an arrangement, the influence of the magnetic field generated around the drive coil 124 can be reduced. A result of measuring the magnetic field of the plurality of Hall elements 130 arranged is output to the calculation unit 150, and the calculation unit 150 calculates the position of the mover 110. In this embodiment, a Hall element is used as the magnetic sensor, but other magnetic sensors such as a magnet diode or a magnetoresistive element may be used.

  Then, the position detection method of the needle | mover 110 is demonstrated. FIG. 3 shows the magnetic field distribution of the mover 110 at the Hall element position of the Hall element 130 used in this embodiment. The vertical axis represents the magnetic field strength, and the horizontal axis represents the stroke position of the mover 110 in the X-axis direction with the arrangement coordinates of the Hall element 130 as the center. For example, when the mover 110 is at a position of −5 mm in the X-axis direction with respect to the Hall element 130, the magnetic field intensity measured by the Hall element 130 is 0.2T. Conversely, when the magnetic field intensity detected by the Hall element 130 is 0.2 T, it can be seen that the mover 110 is at a position of −5 mm in the X-axis direction when viewed from the Hall element 130.

  Since the arrangement coordinates of the Hall element 130 are known, they can be registered in advance as table information. Therefore, if the magnetic field strength is measured by the Hall element 130, the position of the mover 110 is detected by adding the stroke position corresponding to the magnetic field strength to the arrangement coordinates of the Hall element 130 obtained by referring to the table information. can do.

  Here, if the value on the horizontal axis is around 0 mm, the magnetic field strength monotonously decreases, so that the stroke position can be uniquely converted from the magnetic field strength. However, if the stroke position is wider than the monotonously decreasing section, for example, −5 mm or less or 5 mm or more, a plurality of stroke positions correspond to one magnetic field strength.

  Therefore, in the present embodiment, the arrangement intervals of the plurality of Hall elements 130 are arranged at intervals that are narrower than the interval in which the magnetic field intensity output by each of the Hall elements 130 with respect to the distance exhibits a monotone increase or a monotone decrease. When the Hall element 130 having the characteristics shown in FIG. 3 is used, the interval between adjacent Hall elements is set to 10 mm or less because the range from −5 mm to 5 mm is a monotonically decreasing section.

  By arranging in this way, no matter which position the mover 110 moves, any one of the plurality of Hall elements 130 shows the magnetic field strength in a section in which the monotonous increase or monotonic decrease is exhibited. It becomes. Therefore, if the Hall element 130 is used, the position of the mover 110 can be detected in the section showing the monotonous increase or the monotonous decrease, so that accurate position detection can be realized.

  FIG. 4 is a diagram showing an outline of a magnetic field measurement result of the Hall element 130 accompanying the movement of the mover 110. The plurality of Hall elements 130 are arranged at equal intervals, and assigned an arrangement number corresponding to the arrangement position in order from the reference side. In the figure, arrangement numbers 1 to 18 are assigned in order from the left. H and L shown in the figure are logic signals, and each correspond to the Hall element 130 located directly above. Hall element 130 in which the absolute value of the measured magnetic field intensity exceeds a predetermined value is H, and Hall element 130 in which the absolute value of the measured magnetic field intensity does not exceed the predetermined value is L.

  The figure shows changes in logic signals corresponding to the Hall elements 130 when the mover 110 moves from the first stage to the fourth stage in order from the top. In the present embodiment, the predetermined value is a magnetic field strength of 0.01T. Since this value is considered to change appropriately depending on the environment such as the magnetic field strength of the mover 110 and the scale of the linear motor, the value may be appropriately changed and set depending on the environment.

  Most of the logic signals of the Hall elements 130 arranged in the region where the mover 110 faces are H. For some positions where the magnetic field polarity of the mover 110 changes, the magnetic signal intensity may be 0 or a value close to 0, so the logic signal may be L, but at least both ends of the mover 110 have a magnetic field. Therefore, the logic signal becomes H.

  Since the Hall element 130 outside the region facing the mover 110 is away from the magnetic field of the mover 110, its logic signal is L. From this, the arrangement numbers of the Hall elements 130 corresponding to the vicinity of both ends of the mover 110 take the maximum value and the minimum value among the arrangement numbers of the Hall elements 130 whose logic signals are H.

  Then, the Hall element 130 having an arrangement number close to the average value of the maximum value and the minimum value is positioned near the center of the mover 110. Therefore, in the present embodiment, the Hall element 130 having an arrangement number equal to the value obtained by rounding off the average value is determined as a position detection Hall element that detects the position of the mover 110.

  According to the example of FIG. 4, in the first stage at the top, the Hall element 130 corresponding to the left end of the mover 110 is the Hall element indicating the minimum value 1 among the arrangement numbers of the Hall elements 130 indicating H. 130. The hall element 130 corresponding to the right end of the mover 110 is the hall element 130 indicating the maximum value 7 among the arrangement numbers of the hall elements 130 indicating H. Therefore, the arrangement number of the Hall element 130 corresponding to the center of the mover 110 is 4 of these average values. The arrow in the figure indicates the determined Hall element 130. Note that the logic signal of the Hall element 130 with arrangement number 4 is L, which is due to the fact that the magnetic field polarity has changed as described above.

  Similarly, since the minimum value is 2 and the maximum value is 8 in the second stage, the Hall element 130 having the average value of 5 as the arrangement number is determined as the position detection Hall element. In the third stage, the Hall element 130 having the arrangement number 6 is determined, and in the fourth stage, the Hall element 130 having the arrangement number 8 is determined as the position detecting Hall element. Thus, one position detecting Hall element that detects the position of the mover 110 is determined from the arrangement position of the Hall element that has detected magnetism exceeding a predetermined value.

  This determination method depends on the method of magnetization of the mover 110 to be used. In the present embodiment, since the magnetic field intensity is magnetized so as to be symmetrically distributed with the same strength as viewed from the center of the mover 110, the center position of the mover 110 and the center position of the monotonically decreasing or monotonically increasing section. Will almost match. However, when the magnetic field intensity is distributed with different strengths when viewed from the center of the mover 110, the center position of the mover 110 does not coincide with the center of the monotonically decreasing or monotonically increasing section.

  In this case, it is desirable to add this condition when determining the position detecting Hall element. For example, let us assume a case where the center position of monotonic decrease comes not at the center of the mover 110 but at a position 5/8 from the left side. In this case, the Hall element 130 having an arrangement number close to a value obtained by multiplying the sum of the minimum value and the maximum value by 5/8, instead of the average value of the minimum value and the maximum value, is determined as the position detection Hall element.

  FIG. 5 is a flowchart showing a flow of detecting the position of the mover 110. First, in step S51, a current is applied to the drive coil 124, and the mover 110 moves. Next, in step S <b> 52, the change in the magnetic field accompanying the movement of the mover 110 is measured by the Hall element 130. The magnetic field measurement is performed by all the plurality of Hall elements 130 installed on the base member 140. Then, the measured magnetic field strength is transmitted to the calculation unit 150.

  In step S <b> 53, the calculation unit 150 first determines a Hall element 130 whose measured magnetic field strength exceeds a predetermined value among the plurality of Hall elements 130. The predetermined value is set in advance and stored in a storage unit included in the calculation unit 150. Then, the arrangement number of the Hall element 130 whose magnetic field intensity exceeds a predetermined value is acquired. Subsequently, in step S54, the calculation unit 150 first determines the maximum value and the minimum value of the acquired arrangement number. And the value which rounded off the average value of the maximum value and the minimum value is calculated, and the Hall element 130 corresponding to the same arrangement number as this numerical value is determined as a position detection Hall element for detecting the position of the mover 110.

  Finally, in step S55, the calculation unit 150 calculates the position of the mover 110 using the magnetic field strength measured by the position detection Hall element determined in step S54. Details of the position calculation executed in step S55 will be described below.

（１） If the arrangement number of the hall element is i, the arrangement coordinate of the hall element is XS (i), and the stroke position calculated using the determined hall element for position detection is XST, the position X of the mover 110 is expressed by the formula ( It can be calculated in 1).

(1)

Here, the arrangement coordinates of the plurality of Hall elements 130 are stored in advance in the storage unit of the calculation unit 150 as table information as shown in Table 1. When the position detecting Hall element is determined in step S54, the arrangement coordinates of the Hall element can be acquired by referring to the table information with the arrangement number as an input. If the stroke position XST is added to the arrangement coordinates thus obtained, the position of the mover 110 can be calculated. Here, two examples of methods for calculating the stroke position XST are shown.

  As a first example, a technique using a reference table as shown in Table 2 is shown. In this reference table, the stroke position of the mover 110 with respect to the magnetic field strength of the mover 110 measured by the Hall element 130 is registered. Information in the table is measured and registered in advance.

By using this reference table, the magnetic field intensity measured by the Hall element 130 can be converted into the stroke position of the mover 110. That is, the magnetic field strength can be converted into a distance. In the present embodiment, a description will be given of a configuration in which one reference table is held in the storage unit included in the calculation unit 150. However, a reference table corresponding to each Hall element is held corresponding to a difference in characteristics of each Hall element. It may be configured to do so.

  In this method, the calculation unit 150 receives the output of the magnetic field strength measured by the position detection Hall element determined in step S54, and acquires the stroke position by referring to the reference table with the magnetic field strength as an input. . Then, as shown in Formula (1), the mover is obtained by adding the stroke position acquired here and the arrangement coordinates of the position detecting Hall element acquired by referring to the table information shown in Table 1. The position of 110 is calculated.

  Here, it shows more concretely. For example, when the hall element 130 having the arrangement number 3 is determined as the position detection hall element in step S54 and the output of the hall element having the arrangement number 3 is 0.03T, the position of the mover is set to 0.1 mm at −19.5 mm. By adding 60 mm, it can be calculated as −18.1 mm.

  When the position detecting Hall element outputs a value finer than the value registered in the reference table, interpolation is applied to the magnetic field strengths before and after the magnetic field strength registered in the reference table. Correspond with. For example, when the magnetic field intensity output from the position detecting Hall element is 0.035T, a value of 0.70 mm can be acquired by interpolation.

（２） Next, as a second example, instead of using a reference table, a relationship between an output voltage proportional to the magnetic field strength and a stroke position is represented by a conversion function, and a method of using this is described. FIG. 6 is a diagram showing the relationship between the output voltage of the Hall element 130 and the stroke position of the mover 110. The plot represents a value measured and analyzed in advance, and this can be approximated by Equation (2), which is an approximate cubic equation. E indicates the output voltage of the Hall element 130.

(2)

  The values of the coefficients K3, K2, K1, and K0 are calculated by applying the actually analyzed output voltage and stroke position of the Hall element 130 to Equation (2). When these coefficients are applied to the mathematical formula (2), an approximate curve as shown in the figure is drawn and almost coincides with the analysis value. In this method, the value of the coefficient calculated in this way is stored in advance in a storage unit included in the calculation unit 150.

  When the calculation unit 150 receives the output voltage of the position detection Hall element determined in step S54, the calculation unit 150 applies the output voltage and the value of the coefficient stored in the storage unit to the mathematical expression (2). Thus, the stroke position of the mover 110 is calculated. Then, as shown in Equation (1), the position of the mover 110 is obtained by adding the stroke position acquired here and the arrangement coordinates of the position detecting Hall element acquired by referring to the table information shown in Table 1. Is calculated.

  In the present embodiment, accurate position detection of the mover 110 can be realized by adopting the above-described configuration. When the linear motor 100 is used in an environment with a temperature change, it is considered effective to adjust the output by providing a temperature sensor 170 in the vicinity of the Hall element 130.

  For example, by measuring and analyzing the output voltage of the Hall element 130 under various temperature environments, temperature coefficient information is calculated and stored in the storage unit of the calculation unit 150. When the magnetic field is measured by the Hall element 130, a temperature coefficient corresponding to the temperature measured by the temperature sensor 170 is applied. In this way, by taking into account the output of the temperature sensor 170, it is possible to cope with a change in the output voltage of the Hall element 130 due to a change in the ambient temperature, and it is possible to improve the position detection accuracy.

  Moreover, in the said embodiment, although the magnetic field measurement was performed with all the 18 Hall elements 130, it is not restricted to this. For example, the Hall element 130 for magnetic field measurement may be limited to the Hall element 130 within a predetermined range from the determined position detection Hall element.

  As a specific example, a case where the predetermined range is determined to be within the arrangement number 7 will be described as an example. When the Hall element for position detection is a Hall element with arrangement number 7, since the Hall elements corresponding to arrangement numbers 1 to 7 are within a predetermined range, magnetic field measurement is performed and the Hall elements corresponding to arrangement numbers 7 to 13 are also predetermined. Perform magnetic field measurement because it is within range. On the other hand, since the arrangement numbers 14 to 18 are outside the predetermined range, control is performed so as not to execute the magnetic field measurement.

  When the mover 110 moves and the position detecting Hall element is switched to the Hall element having the arrangement number 8, the Hall elements corresponding to the arrangement numbers 2 to 14 are within a predetermined range, and the magnetic field measurement is executed. The Hall elements corresponding to arrangement number 1 and arrangement numbers 15 to 18 do not perform magnetic field measurement. If the predetermined range is appropriately set, there is no problem in position detection. Thus, with this configuration, it is possible to reduce the processing load of the hall element 130 that does not perform magnetic measurement.

  In addition to this, the moving direction of the mover 110 may be considered. By setting the predetermined range separately in the traveling direction and the reverse direction, and setting the predetermined range in the reverse direction smaller than the predetermined range in the traveling direction, further reduction of processing load and power saving are realized. it can. This is because, when attention is paid to the movable element 110 at an arbitrary timing, the direction in which the movable element 110 moves next is more likely to be the traveling direction at that time than the reverse direction. It is desirable to set the predetermined range to a value with a margin in consideration of sudden acceleration of the mover 110, etc., but the margin is adjusted by considering the traveling direction to reduce the processing load. Is realized.

  For example, it is assumed that the predetermined range in the traveling direction is set within the arrangement number 7 and the predetermined range in the reverse direction is set within 5. Similarly to the above-described example, when the position detecting Hall element is the Hall element with the arrangement number 7, and further when the mover 110 has moved in the arrangement number increasing direction, the Hall elements corresponding to the arrangement numbers 1 and 2 Since 130 exceeds the predetermined range 6 in the reverse direction, the Hall element 130 does not execute the magnetic field measurement.

  As a result, the Hall elements corresponding to the arrangement numbers 3 to 13 perform the magnetic field measurement, and the Hall elements corresponding to the arrangement numbers 1 and 2 and the arrangement numbers 14 to 18 do not perform the magnetic field measurement. As described above, by further reducing the number of Hall elements 130 that perform magnetic field measurement by considering the traveling direction of the mover 110, further reduction in processing load and power saving can be realized.

  As mentioned above, although this invention was demonstrated using embodiment, the technical scope of this invention is not limited to the range as described in the said embodiment. It will be apparent to those skilled in the art that various modifications or improvements can be added to the above-described embodiment. It is apparent from the scope of the claims that the embodiments added with such changes or improvements can be included in the technical scope of the present invention.

  The order of execution of each process such as operations, procedures, steps, and stages in the apparatus, system, program, and method shown in the claims, the description, and the drawings is particularly “before” or “prior to”. It should be noted that the output can be realized in any order unless the output of the previous process is used in the subsequent process. Regarding the operation flow in the claims, the description, and the drawings, even if it is described using “first”, “next”, etc. for convenience, it means that it is essential to carry out in this order. It is not a thing.

DESCRIPTION OF SYMBOLS 100 Linear motor, 110 Movable element, 112 Magnet holder, 114 Magnet, 120 Stator, 122 Central axis, 124 Drive coil, 130 Hall element, 140 Base member, 142 Support part, 150 Calculation part, 160 Guide rail, 170 Temperature sensor

Claims (8)

A magnet in which a magnetic pattern for driving is magnetized along a linear driving direction;
A driving coil that is disposed opposite to the magnet and generates a driving force in the driving direction with respect to the magnet;
A linear motor comprising: a plurality of magnetic sensors arranged to face the magnet on the opposite side of the drive coil.   2. The linear motor according to claim 1, wherein an interval between each of the plurality of magnetic sensors is narrower than an interval at which a magnetic field intensity output from each of the plurality of magnetic sensors is monotonously increased or monotonously decreased.   One magnetic sensor that detects the position of the magnet is determined from the arrangement position of the magnetic sensor that has detected magnetism exceeding a predetermined value among the plurality of magnetic sensors, and the output of the one magnetic sensor is calculated to calculate the magnetic sensor. The linear motor according to claim 1, further comprising a calculation unit that calculates a position.   The linear motor according to claim 3, wherein the calculation unit includes a reference table or a conversion function that converts magnetic field strength into distance corresponding to outputs of the plurality of magnetic sensors. A temperature sensor is provided in the vicinity of the magnetic sensor,
The linear motor according to claim 3, wherein the calculation unit calculates the position of the magnet in consideration of an output of the temperature sensor. A magnet magnetized with a driving magnetic pattern along a linear driving direction, a driving coil disposed opposite to the magnet and generating a driving force in the driving direction with respect to the magnet, and the magnet And a position detection method of a linear motor comprising a plurality of magnetic sensors arranged to face each other on the opposite side of the drive coil,
A determination step of determining one magnetic sensor for detecting the position of the magnet from the arrangement position of the magnetic sensor that has detected magnetism exceeding a predetermined value among the plurality of magnetic sensors;
A linear motor position detecting method comprising: calculating a position of the magnet by calculating an output of the determined one magnetic sensor.   The linear motor position detection method according to claim 6, wherein the calculating step calculates the position of the magnet by applying an output of the one magnetic sensor to a reference table or a conversion function for converting magnetic field strength into distance.   The linear motor position detection method according to claim 6, wherein the calculating step calculates the position of the magnet in consideration of an output of a temperature sensor installed in the vicinity of the magnetic sensor.

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