KR102159696B1 - Method and system for linear position sensing using magnetic sensors - Google Patents

Abstract

The linear position detection system according to the present invention is a position detection device that detects a position of a magnet portion in which N poles and S poles are alternately repeated with a period of a distance L, and includes a plurality of magnetic field sensors arranged at intervals of a distance d, the plurality of There are three or more magnetic field sensors, and a distance between the first magnetic field sensor and the last magnetic field sensor among the plurality of magnetic field sensors is L/2 or more.

Description

Method and system for linear position sensing using magnetic sensors}

The present invention relates to a method and system for detecting a linear position using a magnetic field sensor.

In order to detect the position of a mover in a linear motor system, the encoder scale is usually attached to the stator and the encoder head is attached to the mover, so that the encoder head reads the scale of the encoder scale optically or magnetically. Since the linear motor has magnets attached to the stator or mover so that the N and S poles are alternately repeated, if the precision of position detection is not required, a method of detecting the position by reading the magnetic field size of the magnets using a magnetic field sensor is used. I can. The present invention proposes a more efficient and cost-saving method in a method of detecting a position using a magnetic field sensor as described above.

The present invention provides a method and system for detecting a linear position using a magnetic field sensor.

A linear position detection system according to an embodiment of the present invention is a position detection device that detects a position of a magnet portion in which the N pole and the S pole are alternately repeated with a period of a distance L, and includes a plurality of magnetic field sensors arranged at an interval of a distance d. In addition, the plurality of magnetic field sensors are three or more, and a distance between a first magnetic field sensor and a last magnetic field sensor among the plurality of magnetic field sensors is L/2 or more.

In one embodiment, further comprising a processor for calculating the position of the magnet portion based on the magnetic field value of the magnet portion detected by the plurality of magnetic field sensors, the processor, the magnetic field detection value among the plurality of magnetic field sensors It characterized in that the position of the magnet part is calculated based on magnetic field detection values of two adjacent magnetic field sensors having different signs.

In one embodiment, the magnetic field value of the magnet part detected by the plurality of magnetic field sensors is clamped in a partial section of each period.

In one embodiment, a length of a continuous section that is not clamped among the magnetic field values of the magnet part detected by the plurality of magnetic field sensors is 2*d or more.

In one embodiment, the processor may linearly interpolate magnetic field detection values of the two adjacent magnetic field sensors to calculate the position of the magnet part.

In one embodiment, the magnet part is attached to the mover of the linear motor, and the plurality of magnetic field sensors are attached to the stator of the linear motor.

In one embodiment, the plurality of magnetic field sensors are attached to a position close to the movement path of the magnet unit so that the magnetic field of the magnet unit detected by the plurality of magnetic field sensors is clamped.

In the linear position detection method according to an embodiment of the present invention, in a linear position detection method in a linear motor system including a magnet part and a sensor part, a processor is detected by three or more magnetic field sensors included in the sensor part. Receiving the magnetic field value of the magnet unit, and calculating the position of the magnet unit by detecting a position of a point where zero crossing occurs in the received magnetic field value. .

In one embodiment, the step of calculating the position of the magnet part may include calculating the position of the magnet part by linearly interpolating a magnetic field detection value immediately before zero crossing and a magnetic field detection value immediately after zero crossing.

In one embodiment, the magnetic field of the magnet unit is changed in a period of a distance L, and a distance between a first magnetic field sensor and a last magnetic field sensor among the magnetic field sensors is L/2 or more.

In one embodiment, the magnetic field value of the magnet part detected by the magnetic field sensors is clamped in a section where zero crossing does not occur, and the length of a continuous section not clamped among the magnetic field values of the magnet part detected by the magnetic field sensors Is characterized in that at least twice the distance between the magnetic field sensors.

The present invention includes a computer-readable recording medium in which a program for executing a method according to an embodiment of the present invention on a computer is recorded.

According to the present invention, it is possible to provide a method and system for detecting a linear position using a magnetic field sensor efficiently at low cost.

1 is a diagram schematically showing the configuration of a linear position detection system using a conventional magnetic field sensor.
2 is a diagram schematically showing the configuration of a linear position detection system using a magnetic field sensor according to an embodiment of the present invention.
3 is a diagram illustrating that a magnetic field detected by magnetic field sensors is clamped according to an embodiment of the present invention.
4 is a flowchart illustrating a method of detecting a linear position according to an embodiment of the present invention.
5 is a diagram illustrating an example of a magnetic field value detected when a 12-bit ADC is used according to an embodiment of the present invention.
6 to 8 are diagrams illustrating magnetic field sensors arranged at L/8 intervals according to different embodiments of the present invention.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings in order to clarify the technical idea of the present invention. In describing the present invention, when it is determined that a detailed description of a related known function or component may unnecessarily obscure the subject matter of the present invention, a detailed description thereof will be omitted. Constituent elements having substantially the same functional configuration among the drawings are assigned the same reference numerals and reference numerals as possible even though they are indicated on different drawings. If necessary for convenience of explanation, the device and the method will be described together.

1 is a view schematically showing the configuration of a linear position detection system using a conventional magnetic field sensor.

Referring to FIG. 1, in a conventional linear position detection system using a magnetic field sensor, a magnetic field is detected with a magnetic field sensor at a distance where a magnetic field by a magnet is close to a sine wave, but at an interval of L/4, which is 1/4 of the period L of the magnetic field. Two magnetic field sensors are arranged to detect a magnetic field with a phase difference of 90 degrees, and then the position is determined by calculating the phase through arctan operation.

At this time, the magnetic field detected by the magnetic field sensor becomes close to the sine wave, and in order for the magnitude of the sine wave magnetic field to fall within the recognition range of the magnetic field sensor, the magnetic field sensor must be moved away from the magnet. If the magnetic field sensor is moved away from the magnet in this way, the strength of the magnetic field is weakened and the signal-to-noise ratio is lowered. On the other hand, if L=30mm and the required position detection resolution is 1um, in order to obtain the detection values of the two magnetic field sensors with ADC and calculate the arctan in the MCU (microcontroller) to obtain a resolution of 1/30000, even if there is no noise, ADC is required. A 16-bit or higher ADC is required to consider noise and provide margin when matching the magnitude of the sine wave magnetic field within the recognition range of the magnetic field sensor. Using such a high-performance ADC increases the cost of the system.

2 is a diagram schematically showing the configuration of a linear position detection system using a magnetic field sensor according to an embodiment of the present invention.

Referring to FIG. 2, a linear position detection system using a magnetic field sensor according to an embodiment of the present invention includes a magnet unit 100 and a sensor unit 200. In the linear motor, the magnet unit 100 may be attached to the mover and the sensor unit 200 may be attached to the stator, or conversely, the sensor unit 200 may be attached to the mover and the magnet unit 100 may be attached to the stator.

The magnet unit 100 is attached to the magnets 110 so that the N pole and the S pole are alternately repeated with a cycle of a distance L. In the sensor unit 200, a plurality of magnetic field sensors 210 are arranged at intervals of a distance d, and there are three or more magnetic field sensors. Magnetic field sensors are arranged to cover a distance L/2 or more. That is, the distance between the first magnetic field sensor and the last magnetic field sensor among the magnetic field sensors is L/2 or more. For stitching, there can be a 5-10% margin based on L/2.

For example, if L is 30mm, if 9 magnetic field sensors are arranged at 2mm intervals, the distance between the first magnetic field sensor and the last magnetic field sensor is 16mm, so it becomes L/2 or more. 10 can be placed. Hall sensors can be used as magnetic field sensors. The magnets of the magnet unit 100 and the magnetic field sensors of the sensor unit 200 are usually arranged in a straight line, but do not have to.

The magnetic field sensors are arranged close to the movement path of the magnet, so that the magnetic field value of the magnet part detected by the magnetic field sensors is clamped and the zero crossing part is highlighted. In this way, the value of the sensed magnetic field takes the shape of a trapezoid rather than a sine wave. 3 shows that the magnetic field detected by magnetic field sensors is clamped according to an embodiment of the present invention.

By doing so, the position information of the magnet part is obtained by the magnetic field sensors near the zero crossing point, and the signal-to-noise ratio can be significantly increased in the magnetic field sensors. Accordingly, according to the present invention, a low-cost sensor and an ADC can be used, and the cost can be significantly reduced compared to the case of disposing two magnetic field sensors with a 90 degree phase difference as in the prior art. As in the example above, by using 9 or more sensors, the required ADC resolution can be reduced by 3 bits or more, and since the signal-to-noise ratio is high, position sensing is possible even if the ADC performance is low. The magnetic field sensor may comprise an ADC. Using magnetic field sensors with ADCs like this can simplify the system and lower the cost.

In the case of a linear motor (called a long stator motor (LSM) or a moving magnet motor, etc.) in which the magnet part 100 is attached to the mover, a plurality of sensor parts 200 must be attached to the stator, so the cost of the sensor part 200 The need for saving is large, and thus the present invention is particularly useful in a linear motor in which the magnet part 100 is attached to a mover.

Hereinafter, a method of calculating the position of the magnet unit 100 from magnetic field values detected by magnetic field sensors in the linear position detection system according to an embodiment of the present invention will be described with reference to FIGS. 4 and 5. As described above, the magnet unit 100 may be attached to the mover or to the stator, where the position of the magnet unit 100 is the position of the magnet unit 100 viewed from the sensor unit 200, that is, the magnet unit ( It may mean a relative position between 100) and the sensor unit 200.

4 is a flowchart illustrating a flow of a method for detecting a linear position according to an embodiment of the present invention. 5 is a diagram illustrating an example of a magnetic field value detected when a 12-bit ADC is used according to an embodiment of the present invention.

4, magnetic field values detected by magnetic field sensors are converted into digital data by an ADC (not shown), and a processor (not shown) receives a magnetic field value from the ADC (S410), and the received magnetic field value The position of the magnet part 100 is calculated by detecting the position of the point where the zero crossing occurs (S420). That is, the processor detects a position where the magnetic field value detected by the magnetic field sensors changes from positive to negative or from negative to positive. In the example of FIG. 5, a crossing of positive to negative zero occurs between the 4th sensor and the 5th sensor. That is, the processor may calculate the position of the magnet unit 100 based on the magnetic field detection values of two adjacent magnetic field sensors having different magnetic field detection values among the magnetic field sensors.

Since the magnetic field near the zero crossing is close to linear, the processor may linearly interpolate the magnetic field detection value immediately before the zero crossing and the magnetic field detection value immediately after the zero crossing to calculate the position of the magnet unit 100. In the example of FIG. 5, since the detection value of sensor 4 is 1000 and the detection value of sensor 5 is -800, the position of (2mm * 1000/1800) from the position of sensor 4 when the distance between the two magnetic field sensors is 2mm. It can be determined that there is a zero crossing point. If the phase value of the magnet is set as the distance from sensor 0 to the point at which the magnetic field crosses from positive to negative zero, in this case, the phase value of the magnet is (4 * 2mm + 2mm * 1000/1800). If a position crossing from negative to positive zero is detected in the magnetic field detection value, the phase value can be shifted by 15mm, which is L/2. The processor may accumulate the calculated phase value to calculate the position of the magnet unit 100. That is, the processor may rapidly sample the magnetic field (eg, 5 kHz), and when the phase value exceeds one cycle, the position of the magnet unit 100 may be calculated by adding or subtracting L = 30 mm, which is one cycle.

In this way, in order to calculate the position of the magnet unit 100 by interpolating the magnetic field values detected by the two magnetic field sensors before and after the zero crossing, it is necessary to prevent the magnetic field values detected by the two magnetic field sensors before and after the zero crossing from being clamped. The length of the continuous section in which the magnetic field is not clamped must be at least twice the distance between the magnetic field sensors, that is, 2*d or more.

6 to 8 are diagrams illustrating magnetic field sensors arranged at L/8 intervals according to different embodiments of the present invention. In FIG. 6, magnetic field sensors are arranged side by side in one row, but the magnetic field sensors are arranged in two rows as shown in FIG. 7 as needed, such as when the size of the magnetic field sensors is large and it is difficult to arrange them in a desired distance (L/8), or other methods By arranging the sensors, the distance between the two consecutive magnetic field sensors can be a desired distance (L/8), and the magnetic field sensors arranged in this way can be understood to be equivalent to the magnetic field sensors arranged in one row as shown in FIG. have. In addition, as shown in FIG. 8, when the magnet is disposed to be inclined to prevent cogging, the sensor arrangement may also be tilted like a magnet, and the distance between each sensor is determined by the relative distance to the magnet (L/ Since it can be seen as 8), the magnetic field sensors arranged in this way can also be understood to be equivalent to the magnetic field sensors arranged in one row as shown in FIG. 6. Accordingly, the present invention described above can be applied in the same way to the magnetic field sensors shown in the three drawings.

Now, a method of designing a linear position detection system according to the present invention will be described with a specific example.

The final magnetic field detection value output from the ADC is clamped by the smaller of the output range of the magnetic field sensor and the input range of the ADC. Hereinafter, the case where the input range of the ADC is equal to or smaller than the output range of the magnetic field sensor will be described. That is, the magnetic field detection value can have a value in the entire range of the ADC output value.

The position detection resolution can be set from 1/5 to 1/10 of the position control performance. For example, when a position control performance of +/-10um is required, the position detection resolution r=1um can be set.

When the period of the magnet of the magnet part 100 is L, the distance between magnetic field sensors is d, and the number of magnetic field sensors is n, the following equation must be satisfied for the magnetic field sensors to cover the distance L/2 or more.

[Equation 1]

d*(n-1)≥(L/2)

For example, when L=30mm and d=2mm, n≥8.5 should be.

When the length of the continuous section where the magnetic field is not clamped near the zero crossing is k, the following equation must be satisfied to prevent the magnetic field values detected by the two consecutive magnetic field sensors from being clamped.

[Equation 2]

k≥(2*d)

As the ratio p=k/(L/2)=2k/L of the non-clamping section among all sections increases, the linearity of the continuous section without clamping decreases. Therefore, k should be designed to be low in consideration of the error due to nonlinearity. For example, when p=4/15, the error due to linearity can be up to 0.7%.

If the magnetic field in the continuous section that is not clamped is regarded as linear, the difference between the magnetic field detection values by the two magnetic field sensors before and after the zero crossing is the value of the output value range of the ADC multiplied by d/k. Therefore, when using an N-bit ADC, the difference between the magnetic field detection values by the two magnetic field sensors is 2 ^N *(d/k), and the resolution r of the position that can be recognized between the two magnetic field sensors is as follows.

[Equation 3]

r=d/{2 ^N *(d/k)}=k/2 ^N

If k=2d, the resolution r=2d/2 ^N =d/2 ^N-1 , and if d is 2mm and N is 12, the resolution r becomes 1um. In consideration of the linearity error according to the required resolution r and k values, the number of bits of the ADC can be selected in consideration of Equation 3.

Depending on the design, some of the lower bits may be unbelievable depending on the noise or ADC performance, as described above, setting the resolution to about 1/5 to 1/10 of the position control performance and using an internal filter. Can be handled with

The number of bits of the ADC can be selected based on cost. For example, if a 12-bit ADC is inexpensive, you can choose a 12-bit ADC. As technology emerges and higher resolution ADCs are released at lower prices, higher resolution ADCs can be selected.

When the period L of the magnet, the required resolution r, and the number of bits N of the ADC are determined, the distance d between magnetic field sensors is determined in consideration of Equation 2, and the number n of magnetic field sensors may be determined in consideration of Equation 1. When interpolating the magnetic field values detected by the two magnetic field sensors before and after the zero crossing, k can be slightly larger than 2*d so that the detected magnetic field values come in from the boundary of the ADC output value. For example, k can be 2.5*d or less, or 3*d or less. Increasing the number of magnetic field sensors and increasing the ADC resolution can yield finer position resolution, but it is necessary to choose a cost-effective point.

More specifically, a linear position detection system can be designed as follows.

When the position control performance is requested as +/-10um, it can be determined that the position control resolution r is set to 1~2um.

When an inexpensive ADC is about 12 bits, if N=12, r=1um, and k=2*d, d=2mm according to Equation 3. More specifically, when N=12 and r=1um, the length of the non-clamping section becomes k=4mm.In this case, p=2k/L=4/15 is sufficiently small to consider the linearity error near the zero crossing, but r=1 ~2um can be satisfied. If k=2*d, the distance between magnetic field sensors d=2mm can be determined. Even if the distance between the magnet part 100 and the sensor part 200 is adjusted so that the k value is about 5 to 6 mm by setting a margin, r=1 to 2 um can still be satisfied.

When d=2mm, to cover L/2=15mm, the number of magnetic field sensors should be at least 9, but for stitching, the number of magnetic field sensors can be determined as 10.

On the other hand, if the number of sensors within a half cycle (L/2) is n and the ratio p of the non-clamping section out of the entire section, since the non-clamping section must be at least twice the distance between sensors, (L/2) *p≥2*(L/2)/(n-1) to p≥2/(n-1). The number of sensors must satisfy n≥(2/p)+1.

If the non-clamping section is half of the entire section, p=1/2 and n≥5, so the number of sensors within the half cycle must be 5 or more. If the number of sensors within a half cycle is set to 9, when N=9, p≥0.5, so the non-clamping section should be 25% or more of the entire section. If one cycle is 30mm and the distance between magnetic field sensors is 2mm, the number of sensors within half cycle can be considered as n=8.5. In this case, p≥4/15, so the non-clamping section should be about 27% or more of the entire section.

The present invention can also be implemented as computer-readable codes on a computer-readable recording medium. Computer-readable recording media include all storage media such as magnetic storage media and optical reading media.

So far, the present invention has been looked at in detail centering on the preferred embodiments shown in the drawings. These embodiments are not intended to limit the present invention, but are merely illustrative, and should be considered from an illustrative point of view rather than a restrictive point of view. The true technical protection scope of the present invention should be determined not by the above description but by the technical spirit of the appended claims. Although specific terms have been used in the present specification, they are used only for the purpose of describing the concept of the present invention, and not for limiting the meaning or limiting the scope of the present invention described in the claims. Each step of the present invention need not necessarily be performed in the order described, and may be performed in parallel, selectively or individually. Those of ordinary skill in the technical field to which the present invention pertains will understand that various modifications and other equivalent embodiments are possible without departing from the essential technical idea of the present invention claimed in the claims. It is to be understood that equivalents include not only currently known equivalents, but also equivalents to be developed in the future, that is, all components invented to perform the same function regardless of structure.

Claims (12)

As a position detection device that detects the position of the magnet part in which the N and S poles are alternately repeated with a period of a distance L,
It includes a plurality of magnetic field sensors arranged at intervals of distance d,
The plurality of magnetic field sensors are three or more,
The distance between the first magnetic field sensor and the last magnetic field sensor among the plurality of magnetic field sensors is L/2 or more,
Further comprising a processor that calculates the position of the magnet part based on the magnetic field value of the magnet part detected by the plurality of magnetic field sensors,
The processor,
A linear position detection system, characterized in that the position of the magnet part is calculated based on magnetic field detection values of two adjacent magnetic field sensors having different magnetic field detection values among the plurality of magnetic field sensors. delete The method of claim 1,
The linear position detection system, characterized in that the magnetic field value of the magnet part detected by the plurality of magnetic field sensors is clamped in a partial section of each period. The method of claim 3,
Linear position detection system, characterized in that the length of the continuous section that is not clamped of the magnetic field values of the magnet part detected by the plurality of magnetic field sensors is 2*d or more. The method of claim 1,
The processor,
Linear position detection system, characterized in that calculating the position of the magnet by linear interpolation of the magnetic field detection values of the two adjacent magnetic field sensors. The method of claim 1,
The magnet part is attached to the mover of the linear motor,
The plurality of magnetic field sensors are linear position detection system, characterized in that attached to the stator of the linear motor. The method of claim 6,
The plurality of magnetic field sensors,
A linear position detection system, characterized in that the magnetic field of the magnet part detected by the plurality of magnetic field sensors is attached to a position close to the moving path of the magnet part so that the magnetic field of the magnet part is clamped. In the linear position detection method in a linear motor system including a magnet part and a sensor part,
Receiving, by a processor, a magnetic field value of the magnet unit detected by three or more magnetic field sensors included in the sensor unit; And
And calculating, by the processor, the position of the magnet part by detecting a position of a point where zero crossing occurs in the received magnetic field value. The method of claim 8,
The step of calculating the position of the magnet part,
And calculating the position of the magnet part by linearly interpolating a magnetic field detection value immediately before zero crossing and a magnetic field detection value immediately after zero crossing. The method of claim 8,
The magnetic field of the magnet part is changed in a period of distance L,
Linear position detection method, characterized in that the distance between the first magnetic field sensor and the last magnetic field sensor among the magnetic field sensors is L/2 or more. The method of claim 8,
The magnetic field value of the magnet part detected by the magnetic field sensors is clamped in a section in which zero crossing does not occur,
The linear position detection method, characterized in that the length of the non-clamped continuous section among the magnetic field values of the magnetic field detected by the magnetic field sensors is more than twice the distance between the magnetic field sensors. A computer-readable recording medium on which a program for performing any one of claims 8 to 11 is recorded.

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