KR101355636B1 - Position sensor, portable device using the same, and position sensing method thereof - Google Patents

Abstract

The present invention relates to a position sensor, a portable device using the same, and a position sensing method, comprising: a position sensor capable of detecting a position of a moving means provided in a tactile sensor device by measuring an inductance value of a solenoid coil, a portable device using the same, and a position It relates to a detection method. Generating means 110 for generating an electromagnetic field for this purpose; First and second slopes 140 and 150 through which an electromagnetic field flows; A moving means 120 positioned in the air gap 1 between the first and second slopes 140 and 150 and moving according to the action force Fin; And calculation means 130 for calculating a change in the printing value of the generating means 110 as the area between the first and second inclined surfaces 140 and 150 and the moving means 120 changes due to the movement of the moving means 120. Disclosed is a position sensor using a change of a print value, characterized in that the position of the moving means 120 can be sensed.

Description

Position sensor, portable device using the same, and position sensing method

The present invention relates to a position sensor, a portable device using the same, and a position sensing method, and more particularly, to a position sensor capable of detecting a position of a moving means provided in a tactile actuator device by measuring an inductance value of a solenoid coil. It relates to a portable device and a location sensing method.

In general, tactile sensation is a tactile sensation that can be felt by a human finger or stylus pen when touching an object, and encompasses tactile feedback that is felt when the skin touches the surface of the object and muscle sense feedback when the movement of joints and muscles is disturbed. Concept.

Conventional devices for conveying this tactile sense are shown in FIGS. 1 and 2. The invention shown in FIG. 1 is a stiffness generating device, and the invention shown in FIG. 2 is a resistive force generating module (proportional solenoid structure) using an inclined surface. In order to generate the tactile feedback, the necessity of knowing the position of the contact plate 11 or the force transmission means 21 changed according to the applied force Fin arises. The reason for this is to generate a signal capable of transmitting various tactile sensations according to the pressed depth to deliver tactile feedback to the user.

Therefore, in the technical field to which the present invention belongs, it has been required to develop an invention capable of sensing the position of the moving means provided in the resistance generating module using the conventional rigidity generating device or the inclined surface.

Accordingly, the present invention has been made to solve the problems described above, and provides an invention that can detect the position of the moving means by measuring the inductance value of the solenoid coil provided in the conventional tactile generating device. have.

However, the objects of the present invention are not limited to the above-mentioned objects, and other objects not mentioned can be clearly understood by those skilled in the art from the following description.

The object of the present invention described above is a generating means 110 for generating an electromagnetic field; First and second slopes 140 and 150 through which an electromagnetic field flows; A moving means 120 positioned in the air gap 1 between the first and second slopes 140 and 150 and moving according to the action force Fin; And calculating means 130 for calculating a change in the printing value of the generating means 110 as the distance of the air gap 1 changes due to the movement of the moving means 120. It can be achieved by providing a position sensor using a change in the factor value characterized in that it can detect.

In addition, the generating means 110 is characterized in that for generating an electromagnetic field by using a solenoid coil.

The printing value may be an inductance value of the solenoid coil or a voltage value of both ends of the solenoid coil.

And, the changed distance of the air gap 1 is characterized in that the distance formed in the path through which the electromagnetic field passes.

On the other hand, the object of the present invention generating means 210 for generating an electromagnetic field; Moving means 220 for moving on the path of the electromagnetic field in accordance with the action force (Fin); And calculating means 230 for calculating a change in the print value of the generating means 210 as the area of the moving means 220 existing on the path is changed by the movement of the moving means 220. It can be achieved by providing a position sensor using a change in the factor value, characterized in that the position of 220 can be detected.

In addition, the generating means 210 is characterized in that for generating an electromagnetic field using a solenoid coil.

The printing value may be an inductance value of the solenoid coil or a voltage value of both ends of the solenoid coil.

On the other hand, the object of the present invention generating means 310 for generating an electromagnetic field; First and second slopes 340 and 350 through which an electromagnetic field flows; A moving unit 320 positioned in the air gap 1 between the first and second slopes 340 and 350 and moving in accordance with the action force Fin; And a microprocessor 330 for calculating a position of the moving means 320 by calculating a change in the printing value of the generating means 310 as the distance of the air gap 1 changes due to the movement of the moving means 320. It can be achieved by providing a portable device comprising a.

In addition, the microprocessor 330 is characterized in that for outputting a signal for generating the tactile feedback to the generating means 310 according to the calculated position of the movement means (320).

The signal may be a signal selected from at least one of a waveform type, an amplitude size, and a frequency as a control variable, or a combination of control variables.

On the other hand, the object of the present invention generating means 410 for generating an electromagnetic field; A moving means 420 moving along the path of the electromagnetic field according to the action force Fin; And a micro to calculate the position of the moving means 420 by calculating a change in the printing value of the generating means 410 as the area of the moving means 420 existing on the path is changed by the movement of the moving means 420. It can be achieved by providing a portable device comprising a processor (430).

In addition, the microprocessor 430 may output a signal for generating tactile feedback to the generating means 410 according to the calculated position of the moving means 420.

The signal may be a signal selected from at least one of a waveform type, an amplitude size, and a frequency as a control variable, or a combination of control variables.

On the other hand, an object of the present invention is to move the moving means (120,220) placed on the path of the electromagnetic field as another category (S610); Changing the distance or area of the air gap 1 or the moving means 120 or 220 by the movement of the moving means 120 or 220 (S620); Calculating, by the calculating means (130,330), a change in the print value of the generating means (110,210) according to the changed distance or area (S630); And calculating (130) the calculation means (130, 330) of the movement means (120, 220) can be achieved by providing a position sensing method using a change in the factor value.

The printing value may be an inductance value of the solenoid coil or a voltage value of both ends of the solenoid coil.

And, the distance of the changed air gap 1 or the area of the changed means 120 is characterized in that the distance or area formed in the path through which the electromagnetic field passes.

According to the present invention as described above has the effect of detecting the position of the moving means by measuring the inductance value of the solenoid coil provided in the haptic generating device.

In addition, according to the present invention, there is no need for other means for detecting the position of the moving means, thereby reducing the cost and efficiently detecting the position.

BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate preferred embodiments of the invention and, together with the description, serve to further the understanding of the technical idea of the invention, It should not be construed as limited.
1 is an exploded perspective view of a stiffness generating apparatus according to the present invention,
2 is a resistance generation module using an inclined surface according to the present invention,
3 is a conceptual diagram for obtaining a voltage across the solenoid coil according to the present invention,
4 and 5 is a configuration diagram showing the configuration of a position sensor according to a first embodiment of the present invention,
6 is a view showing the pressure difference of the solenoid coil according to the first embodiment of the present invention,
7 and 8 are configuration diagrams showing the configuration of a position sensor according to a second embodiment of the present invention,
9 is a configuration diagram for measuring voltage values at both ends of a solenoid coil according to first and second embodiments of the present invention;
10 and 11 are diagrams showing the configuration of a portable device according to the first and second embodiments of the present invention.
12 is a perspective view of a position sensor coupled to a portable device according to the first and second embodiments of the present invention;
13 is a flow chart sequentially showing the order of the position detection method according to the present invention.

Hereinafter, a preferred embodiment of the present invention will be described with reference to the drawings. In addition, the embodiment described below does not unduly limit the content of the present invention described in the claims, and the entire structure described in this embodiment is not necessarily essential as the solution means of the present invention.

< Of the first embodiment  Configuration>

First, as shown in FIG. 3, excitation of a cosine wave to a solenoid coil causes the magnitude of the voltage at both ends of the solenoid coil to develop as follows.

Here, R ₁ is the resistance component of the solenoid coil, and R ₀ is the internal resistance of the frequency generator for generating the cosine wave.

Therefore, it can be seen that the voltage across the solenoid coil changes according to the inductance L [H] value. In this case, the inductance L [H] value is developed as shown in Equation 2 below.

는 투자율, N²은 솔레노이드 코일 턴수, A는 솔레노이드 코일의 단면적,

은 솔레노이드 코일의 높이이다.
here,

Is the permeability, N ² is the number of turns of the solenoid coil, A is the cross-sectional area of the solenoid coil,

Is the height of the solenoid coil.

)이 변하면 인덕턴스 L이 변함을 알 수 있고, 인덕턴스 L이 변함에 따라 인덕턴스 코일의 양단 전압이 변할 수 있다. 이러한 원리를 바탕으로 본 발명에 따른 제1실시예 및 제2실시예를 설명하기로 한다.
In conclusion, when [Equation 1] and [Equation 2] are combined, the permeability (

It can be seen that when the) changes, the inductance L changes, and as the inductance L changes, the voltage across the inductance coil may change. Based on this principle, a first embodiment and a second embodiment according to the present invention will be described.

As shown in FIG. 4, the position sensor using the change of the factor value according to the first embodiment of the present invention has approximately the generating means 110, the first and second slopes 140 and 150, the moving means 120, and the calculating means. 130 can be configured. Hereinafter, the position sensor using the change of the factor value according to the first embodiment of the present invention will be described with reference to FIGS. 3 and 4.

As shown in FIG. 4, the generating means 110 according to the first embodiment of the present invention is a means for generating an electromagnetic field. In order to generate an electromagnetic field, a solenoid coil and an iron core (not shown) are generally provided to generate an electromagnetic field. At this time, the direction of the electromagnetic field can be changed by changing the direction of the current.

Meanwhile, the magnetorheological fluid 3 is filled between the first inclined plane 140 and the moving unit 120 or between the second inclined plane 150 and the moving unit 120 by the electromagnetic force generated by the generating unit 110. It provides the user with damping force (resistance, opposite to the direction in which the fin is applied). The damping force can be changed to generate tactile feedback (resistance, vibration sense) by inputting a periodic signal to be described later.

Here, the magnetorheological fluid is one of intelligent materials as a material in which the viscosity characteristic of the fluid is reversibly changed according to the strength of the magnetic field. Specifically, the magnetorheological fluid includes iron, nickel, cobalt, and magnetic alloys of fine particles having a diameter of several to several tens of microns in a dispersion medium such as mineral oil, synthetic hydrocarbon, water, silicone oil, and esterified fatty acid. Refers to a dispersed noncolloid suspension.

On the other hand, the magnetorheological fluid has a large variation in flow characteristics such as viscosity characteristics of the fluid as the magnetic field is applied, and excellent durability. In addition, they are relatively less sensitive to contaminants and are very fast and reversible to magnetic fields. Because of this property, it is considered to have great applicability in various industrial fields such as vibration control devices such as clutches of automobiles, engine mounts, dampers, high-rise seismic devices, and driving devices of robotic systems.

In addition, magnetorheological fluids exhibit the properties of Newtonian fluids when no magnetic field is applied. However, when a magnetic field is applied, the dispersed particles form a dipole to form a fibrous structure in a direction parallel to the applied magnetic field, and the fibrous structure increases the viscosity and thus has a shear force or a resistance to flow that interferes with the flow of the fluid. Increase the yield stress much. At this time, the yield stress increases with the strength of the magnetic field.

On the other hand, when the generating means 110 uses a solenoid coil, such a solenoid coil has an inductance value (L). As shown in FIG. 5, when the moving means 120 to be described later moves downward by a force Fin, the distance of the air gap 1 passing through the electromagnetic field (x _1- > x ₂ , x ₁ '->). x ₂ ') is reduced compared to FIG.

)이 변화된다. 즉 도 4의 투자율을

라 하고, 도 5의 투자율을

라 하면 다음의 [수학식 3]과 같다.
At this time, if the distance of the air gap (1) through which the electromagnetic field passes, the permeability (

) Is changed. That is, the permeability of FIG. 4

The permeability of FIG.

If it is as follows [Equation 3].

)의 변화에 따른 도 4 및 도 5의 인덕턴스 코일의 전압차는 다음의 [수학식 4]와 같이 전개된다.
Therefore, L _B > L _A , and as shown in FIG. 6, it can be seen that the voltage at both ends of the inductance coil is changed by Equation 1. Where the permeability (

The voltage difference between the inductance coils of FIGS. 4 and 5 according to the change of) is developed as shown in Equation 4 below.

The first and second slopes 140 and 150 according to the first embodiment of the present invention are sloped surfaces through which an electromagnetic field flows. In this case, the second inclined surface 150 is positioned to face the first inclined surface 140. The structure that generates resistance by using the inclined surface is called proportional solenoid structure.

The moving means 120 according to the first embodiment of the present invention is located in the air gap 1 between the first and second inclined surfaces 140 and 150 and moves upward and downward in accordance with the action force Fin. As the moving means 120 moves in the vertical direction, the distance of the air gap 1 through which the electromagnetic field passes changes as shown in FIGS. 4 and 5.

As one embodiment of the moving means 120 may be a plunger (not shown). The plunger moves in the up and down direction according to the working force Fin, and an electromagnetic field may flow.

)이 변화되고, 투자율의 변화에 따라 인덕턴스 값이 변하고, 인덕턴스 값의 변화에 따라 인덕턴스 코일 양단의 전압 값을 검출하여 이동수단(120)의 눌려진 깊이(위치)를 감지한다. 에어 갭(1)의 거리는(도 4에서 x₁,x₁') 제1경사면(140)과 이동수단(120) 사이 또는 제2경사면(150)과 이동수단(120) 사이의 전자기장이 통과하는 거리이다.The calculating means 130 according to the first embodiment of the present invention detects the pressed depth (position) of the moving means 120 by detecting a change in the printing value of the generating means 110. That is, as the distance of the air gap 1 changes according to the vertical movement of the moving means 120, the permeability (

), The inductance value changes according to the change of the permeability, and the pressed depth (position) of the moving means 120 is detected by detecting the voltage value across the inductance coil according to the change of the inductance value. The distance of the air gap 1 (x ₁ , x ₁ ′ in FIG. 4) is such that an electromagnetic field passes between the first inclined plane 140 and the moving means 120 or between the second inclined plane 150 and the moving means 120. Distance.

In this case, the factor value may detect the position of the moving unit 120 by sensing the inductance value according to the change of the permeability, and the factor value may be the voltage across the inductance coil according to the change of the inductance value.

In this case, the voltage across the inductance coil calculates the voltage across the inductance by applying a predetermined waveform (a periodic waveform, such as excitation wave, sawtooth wave, etc.) to the solenoid coil. The voltage across the solenoid coil is preferably converted into a DC voltage by the peak detector 90 and input to the calculation means 130 to be calculated. Therefore, the calculation means 130 may detect the position of the moving means 120 according to the change of the DC voltage value (the amplitude change amount of the waveform applied to the solenoid coil).

< Of the second embodiment  Configuration>

As shown in FIG. 7, the position sensor using the change of the factor value according to the second embodiment of the present invention may be composed of the generating means 210, the moving means 220, and the calculating means 230. . Hereinafter will be described based on the change in inductance of the solenoid coil according to the change of the permeability described above.

As shown in FIG. 7, the position sensor using the change of the print value according to the second embodiment of the present invention has the same principle as the position sensor using the change of the print value according to the first embodiment described above. Therefore, only parts different from the first embodiment will be described.

The moving unit 220 according to the second embodiment of the present invention moves in the vertical direction in response to the action force Fin on the path of the electromagnetic field. As shown in FIG. 7, when the moving means 220 is separated from the generating means 210 generating the electromagnetic field, the area of the moving means 220 through which the electromagnetic field passes is smaller than the area shown in FIG. 8.

)이 변하게 된다. 즉 도 7의 투자율을

라하고, 도 8의 투자율을

라 하면 다음의 [수학식 5]와 같다.
In this case, when the area of the moving means 220 existing on the path of the electromagnetic field is changed, the above-described permeability (

) Will change. That is, the permeability of FIG.

D, the permeability of FIG.

If it is as follows [Equation 5].

Therefore, it can be seen that the voltage across the inductance coil is changed by Equation 1, and the voltage value across the inductance coil is different according to Equation 4.

Meanwhile, as an embodiment of the generating unit 210 and the moving unit 220, the yoke 14 corresponds to the moving unit 220, and the solenoid coil 16 is the generating unit ( 210). Therefore, when a working force Fin is applied to the contact plate 11, the yoke 14 moves downward, and as the downward movement moves downward, the yoke 14 is placed on the path of the electromagnetic field generated by the solenoid coil 16. The area becomes large. When the area of the yoke 14 changes, the permeability changes and the inductance value of the solenoid coil 16 changes.

Meanwhile, the magnetorheological fluid 15 shown in FIG. 1 is filled between the yoke 14 and the solenoid coil 16 to damp the force (resistance force, force) by the electromagnetic force generated by the generating means 210. Opposite to the direction in which it acts). The damping force can be changed to generate tactile feedback (resistance, vibration sense) by inputting a periodic signal to be described later.

The calculating means 230 according to the second embodiment of the present invention detects the change in the voltage value of both ends of the solenoid coil of the generating means 110 in the same manner as the calculating means 130 according to the first embodiment of the present invention described above. To detect the pressed depth (position) of the moving means (220).

The position sensors according to the first and second embodiments described above may be applied using the conventional rigidity generating device 10 or the resistive force generating module 20 using an inclined surface. That is, the stiffness generating device 10 or the resistive force generating module 20 using the inclined surface may generate tactile sensations by exciting various types of waveforms.

In this case, the generating means 110 and 210 and the moving means 120 and 220 are provided in order to provide a variety of tactile sensations according to the positions of the moving means 120 and 220. The position of the vehicle can be detected.

< Solenoid  Both ends of the coil Voltage value  Measuring Device>

In order to measure the voltage value of both ends of the solenoid coil as shown in FIG. 9, first, a DC voltage is generated in the DAC converter 41 by the control signal of the control means 30, and 0 to 250 Hz in the waveform generator 43. Generates square or cosine waves in the frequency range. In addition, the cosine wave generator 45 generates the cosine wave of about 1 to 2 kHz by the control means 30.

In this case, the DC voltage of the DAC converter 41 is for generating a sense of muscle and the waveform generator 43 is for generating a sense of vibration. In addition, the cosine wave generator 45 is a signal for detecting the voltage value of both ends of the solenoid coil.

The multiplex 50 receives one of the above-described output signals of the DAC converter 41 and the waveform generator 43 and selects one of the signals for generating vibration or muscle sense. When the selected signal and the signal generated by the cosine wave generator 45 are synthesized by the synthesizer 55 and input to the stiffness generating device 10 or the resistive force generating module 20 using the inclined surface through the current amplifier 60, the sense of vibration is sensed. Or generate muscle sense.

As an example, if a signal of 100 Hz is output from the waveform generator and is selected by the multiplexer, and the cosine wave generator 45 generates a frequency of 1 kHz, the signal before passing through the frequency generator internal resistance 47 and being input to the band pass filter 70 is shown. Is a superposition signal of 1kHz and 100Hz.

볼트인 경우 피크 디텍터(90)는 10볼트의 DC값을 감지한다.
The bandpass filter 70 detects only a signal of 1 kHz (since a signal of 1 kHz is a signal representing the voltage value of both ends of the solenoid coil) and outputs it to the amplifier 80, and the amplifier 80 amplifies the 1 kHz signal. When the peak detector 90 detects the amplified peak value of 1 kHz and inputs it to the control means 30, the control means 30 may recognize the positions of the moving means 120 and 220. At this time, the amplitude of 1kHz

In the case of volts, the peak detector 90 senses a DC value of 10 volts.

<Configuration of the portable device>

10 and 11, the portable device according to the present invention includes a position sensor according to the first and second embodiments described above. At this time, the microprocessor 330 provided in the portable device detects the positions of the moving means 120 and 220 in place of the above-described calculation means 130 and 230.

However, the microprocessor 330 is configured together with the calculation means 130 and 230 to receive the location of the movement means recognized by the calculation means 130 and 230 to generate various tactile feedback depending on the type of application or button that is being executed in the portable device. It is also possible to output the signal (waveform according to one waveform selected according to the type of waveform, amplitude size, frequency or a combination thereof) to the stiffness generator 10 or the like. Hereinafter, the generating means, the moving means, and the first and second slopes are the same as described above, and thus description thereof will be omitted.

As shown in FIG. 12, the stiffness generating device 10 is coupled to a portable device. The portable device 2 including the stiffness generating device 10 may be applied to a smartphone, a PDA, a notebook, a tablet PC, or the like. In addition, it can be applied to a console game console, a keyboard, a joystick, a remote controller or a stylus pen to transmit tactile feedback to a user.

<How to detect location>

As shown in Figure 13, the position detection method according to the present invention is as follows. First, the moving means (120,220) placed on the path of the electromagnetic field is performed to move downward according to the action force (Fin) (S610).

Next, in the case of the resistance generation module 20 using the inclined surface, the area of the air gap 1 placed on the path of the electromagnetic field is changed by the movement of the moving means (120, 220) (S620). On the other hand, in the case of the stiffness generating device, the area of the moving means (120,220) (yoke) placed on the path of the electromagnetic field is changed (S620).

Next, the calculation means (130, 330) performs a step (S630) for calculating a change in the print value of the generating means (110,210) according to the changed area. In detail, as the area of the air gap 1 or the moving means 120 and 220 changes, the permeability changes. The changed permeability changes the inductance value of the solenoid coil as shown in [Equation 2].

As shown in Equation 1, the changed inductance value changes the voltage value of both ends of the solenoid coil which is a factor value.

Finally, the calculation means (130, 330) detects the position of the moving means (120, 220) according to the voltage value of both ends of the changed solenoid coil (S640). That is, the voltage values (DC values) at both ends of the solenoid coil according to the positions of the moving means 120 and 220 may be stored in the lookup table, and the positions of the moving means 120 and 220 may be detected based on the lookup table value.

Although the present invention has been described with reference to the embodiment thereof, the present invention is not limited thereto, and various modifications and applications are possible. In other words, those skilled in the art can easily understand that many variations are possible without departing from the gist of the present invention.

1: air gap
2: portable device
3: magnetorheological fluid
10: stiffness generator
11: contact plate
12: cover
13: Piston
14: York
15: rheological fluid
16: solenoid coil
17: spring
18: Housing
20: resistance generation module using the inclined surface
21: power transmission means
30: Control means
41: DAC Converter
43: waveform generator
45: cosine wave generator
47: cosine wave generator internal resistance
50: multiplexer
55: synthesizer
60: current amplifier
70 band pass filter
80: amplifier
90: peak detector
110: generating means
120: means of transportation
130: calculation means
140: first slope
150: second slope
210: generating means
220: Moving means
230: calculation means
330: microprocessor
430: microprocessor

Claims (22)

Generating means for generating an electromagnetic field;
First and second slopes through which the electromagnetic field flows;
Moving means positioned in the air gap between the first and second inclined surfaces and moving according to an action force Fin; And
Calculation means for calculating a change in the printing value of the generating means as the distance of the air gap between the first and second inclined surfaces and the moving means is changed by the movement of the moving means. Can detect
The changed distance of the air gap is a position sensor using a change of the print value, characterized in that the distance formed in the path through which the electromagnetic field passes.
The method of claim 1,
The generating means is a position sensor using a change of the print value, characterized in that for generating the electromagnetic field using a solenoid coil.
3. The method of claim 2,
The factor value is a position sensor using a change of the factor value, characterized in that the inductance value of the solenoid coil or the voltage value of both ends of the solenoid coil.
delete The method of claim 1,
And the calculating means calculates an amplitude change amount of the waveform according to the change of the printing value by applying a predetermined waveform to the generating means.
The method of claim 1,
A magnetorheological fluid is filled between the air gaps to provide a damping force to the user by the electromagnetic force generated by the generating means.
delete delete delete delete delete Generating means for generating an electromagnetic field;
First and second slopes through which the electromagnetic field flows;
Moving means positioned in the air gap between the first and second inclined surfaces and moving according to an action force Fin; And
A microprocessor for calculating the position of the moving means by calculating a change in the printing value of the generating means as the distance of the air gap between the first and second inclined surfaces and the moving means is changed by the movement of the moving means; Portable device comprising a.
13. The method of claim 12,
The microprocessor,
And a signal for generating tactile feedback according to the calculated position of the moving means to the generating means.
The method of claim 13,
The signal is,
And at least one of a waveform type, an amplitude size, and a frequency as a control variable, or a combination of the control variables.
13. The method of claim 12,
A magnetorheological fluid is filled between the air gaps so that the microprocessor continuously changes the damping force of the magnetorheological fluid to provide tactile feedback to the user.
Generating means for generating an electromagnetic field;
Moving means for moving on the path of the electromagnetic field according to an action force Fin; And
And a microprocessor for calculating a position of the moving means by calculating a change in the printing value of the generating means as the area of the moving means existing on the path is changed by the movement of the moving means. Portable device.
17. The method of claim 16,
The microprocessor,
And a signal for generating tactile feedback according to the calculated position of the moving means to the generating means.
The method of claim 17,
The signal is,
And at least one of a waveform type, an amplitude size, and a frequency as a control variable, or a combination of the control variables. delete delete delete delete

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